Regarding death toll, an overview by Purkait et al (2020) reaches the following conclusions:

There were approximately 25 major famines during the British rule in India, spread all over the States and regions of India. The incidence of severe and repeated famine reached its numerically deadly peak during the late 18th and whole of 19thcenturies. Administrators of British India were bad enough to allow remarkable impact on the long term population growth of the country. Famines in India resulted in more than 60 million deaths over the course of the 18th-20th centuries, and only the Great Bengal famine of 1770 is estimated to have taken the lives of nearly 10 million people. However, 30-40 million Indians were the victims of famines in the latter half of the 20th century. (p. 62)

The tweet you linked falls prey to a common confusion about British rule in India: specifically, the British Raj ruled only between 1858 and 1947. If we speak about British rule more generally, beginning in the mid 18th century with the consolidation of the British East India company over most of modern day India, we can tabulate a figure of roughly 60 million deaths during the period of British rule in India. However, the culpability of the British in each famine varies wildly, and most scholarship analyzing British rule as a catalyst of famine tends to focus on famines within the Raj period, specifically the Great Famine of 1876-78, 1896-1902 famine, and the Bengal famine of 1943. Notably, Purkait et al, when enumerating famines under British rule, identify "British policies" as catalysts only in these three instances. If we take this analysis at face value and rely on mortality estimates from Purkait et al, this produces a figure of 13.6-23.3 million famine deaths for which British rule bore partial responsibility.

Before moving on, I'd like to note that Mike Davis attempted a similar tabulation in Late Victorian Holocausts, and his summation of various academic mortality estimates suggests 12.2-29.3 million deaths for the 1876-9 and 1896-1902 famines (p. 7). It bears noting that his analysis excludes the Bengal Famine of 1943 altogether. So, if we accept the premise that the British bore responsibility for these famines, then they were indeed responsible for tens of millions of deaths, though not 80 million as the tweet claims.

This brings us to the thornier aspect of the debate: to what extent did Britain bear responsibility for famines in colonial India? In the late 20th century, a number of revisionist historians began to revisit the role of the British colonial state in the famines of the 19th and 20th centuries. This analysis - initially popularized by BM Bhatia (see: Famines In India, 1963) and Nobel-prize-winning economist Amartya Sen - suggests that the undemocratic nature of British colonial rule, in conjunction with a push to commercialize Indian agriculture, exacerbated famines caused by natural factors. As Amartya Sen and Mike Davis have detailed, the British Raj in the late 19th century sought to totally upend the Indian agricultural system, pushing away from traditional subsistence-based modes of production and towards a more commercialized model with an emphasis on exports and cash crops.

An article by A.C. Sahu examines how British-mandated grain exports played a major role in instigating both the 1876-9 and 1896-1902 famines. The export of grain became so problematic that prominent British Indian officials began a temporary moratorium on grain exports in 1866, though British officals rebuked them:

In spite of the severe famine in North-Western Provinces Raja- putana and Punjab in 1868-69, the export had gone up to 752,560 tons.

...

Even officials at the helm of affairs did not appreciate such large- scale export of rice. The Lieutenant Governor of Bengal C. Beadon in a minute dated 28 November 1866 observed that it was an actual and undeniable fact that while thousands of poor people in Bengal and Orissa had starved during the last few months, hundreds of thousands of mounds had been exported at a profit to foreign countries.

...

When the Government of India turned down his proposal to stop the export of rice from Bengal, which was in the grip of a terrible famine, Campbell noted : "I have no doubt that in any other country, than a British-governed country, it would have been done". He further added : "Lord Northbrook, bred in the strictest sect of English free-traders, looked on my proposal as a sort of abominable heresy". (Sahu, p. 811).

This becomes a common theme when analyzing British response to famine during the period. When Sir Richard Temple, the Lieutenant Governor of Bengal, successfully averted a nascent famine in Bihar in 1874 through the mass import of rice from Burma, British officials admonished him for associated costs. Hall-Matthews (2007) highlights how Temple subsequently revised his famine response models to prioritize low expenditure, producing woefully inadequate responses to the 1876 famine:

In January 1877, after 2 weeks inspecting relief works in Madras, Temple provoked the biggest controversy of the famine campaign by suggesting that the governments of Madras and Bombay should experiment with a reduced relief wage, which for men was sufficient to purchase 1 pound of grain per day. The argument that they should be granted the smallest amount possible for survival was justified by the supposition that offering over-generous wages would 'demoralise', and reduce people's inclination to industry, a theory which he himself had scoffed at in 1874 and was to reject again after returning to England.'2 His greater aim was to look for ways of saving the state's money, remarking in Gladstonian fashion that it would be unjust to the public interest to exceed the minimum need. (Hall-Matthews, p. 1193)

Certain scholars - notably Tirthankar Roy - have sought to attribute the lackluster British response to the 1876 famine to a lack of necessary infrastructure, but analysis of the primary source documents reveals that, whatever impediment infrastructure may have posed, British officials simply did not care enough to implement effective policies to circumvent famine. This owed both in part to profit motives (namely, continued export of grains and cultivation of cash crops) as well as the prevalence of Malthusian ideology among the British elite, as outlined by Mike Davis.

(CONTINUED IN SECOND POST)

Well happily, questions similar to yours have been asked before, see:

Were famines in India a form of genocide ? this answer specifically discusses Mike Davis and the comment linked in question is very similar to the tweet you posted.

How many died in because of the British in India? by u/davepx

More recently see u/lordneobic 's wonderful answer to the question Did the American Civil War technically lead to The British starving people in India?

It's worth quoting parts of his answer:

According to an Indian government report on the 1866 famine suggests an average of 15 million acres of dry land and a further 5 and a half million acres of irrigated land were used to grow food from 1861 to 1866 which was enough to provide a food surplus for most of these years, including the period of greatest cotton production. So why did it suffer a famine? Drought.

Drought was a common problem in India. Much of India relied on the monsoons for water, and if they failed, or were inconsistent famine would follow. This was a problem that governments through all of Indian history had to contend with, and the British were no exception. The British had made great strides in their famine response since the Great Bengal Famine in the 1770s but the limits of transportation and budget made any famine deadly.

But famine in this period was caused by crop failure, not British demands for a certain crop.

Not directly related but illuminating nonetheless, see this wonderful conversation involving the legendary Zhukov:

Has India since it gained it's independence suffered from famine?