From my reading, it seems like it had a lot to do with the Sino-Japanese War and Empress Cixi's personality - is this what historians believe? Is it even possible to pick out a 'point of no return' in the first place?
Personally, I think the humiliating defeat to a "dwarf barbarian" was the point of no returns, as it clearly exposed the flaws of the Self Strengthening Movement (SSM) and Cixi's conservative mindset and failure to implement any radical reforms meant that the underlying root causes would always be present in the Qing society. Cixi was extremely narcassistic and in fact arrogant, her pride and public image seemed more important than the eradication of the Qing problems. Her efforts with the SSM were clearly just papering over the cracks and the defeat in SJW highlighted this. However, people may argue that the efforts were made post Boxer Rebellion (BR) with the Late Qing Reforms (LQR), but again these were half-hearted reforms that didn't actually show any tangible change, and by this point, it was Too Much Too Late and even the scholar-gentry were forced to question the legitimacy of the Qing. Would it be fair to say that the point of no returns was the SJW as it highlighted Cixi's lack of ambition and conservative ideals, and the BR simply expedited the fall of the Qing as it paved the way for Sun Yat-Sen too capitalise on the public unrest and carry out the Xinhai Revolution 1911?
Thanks in advance
To ascribe the fall of the Qing Dynasty primarily to the Empress Dowager Cixi perhaps takes too much of an individual-focussed and medium-term view of what happened. For sure, the damage to Qing rule under Cixi's auspices was considerable, but for one cannot be solely ascribed to Cixi, and for another (and more importantly) should in my view be seen to a great extent as the tip of an iceberg, the core of which had been in formation for much longer. Whilst I have written a reasonably broad answer regarding the fall of the Qing previously (see here) I will do something more directly structured as per the question's wording in this case, although before going into the core section I will do a little bit in terms of addressing some issues in the elaboration to the question itself, as there are a few potential misconceptions to correct here that would be awkward to fit in later and also provide some framing for the answer as a whole.
The Problem of Blaming Cixi
One key problem with blaming the Empress Dowager is that, well, how much did she actually do? I will firmly admit now to being someone who places a high value on individual agency in history, but to think of Cixi as having been the chief actor in the disappointment of the Self-Strengthening Movement obscures that the SSM was to a great extent carried out not by the central government but rather by regional strongmen. The likin transport and commercial tax that bankrolled a lot of these activities (land taxes having been frozen since the time of the Kangxi Emperor at the turn of the eighteenth century) was placed entirely under the jurisdiction of proto-warlords and similar like Li Hongzhang and Zuo Zongtang, and the establishment of modern military arsenals was also very much a province-level endeavour. When looking at the failure of the Qing fleets in the Sino-French and Sino-Japanese Wars, let it not be forgotten that their commanders consistently refused to support each other by 'declaring neutrality' in these international conflicts.
The Nature of the Xinhai Revolution
As Joseph Esherick's seminal Reform and Revolution in China showed in 1976, the Xinhai Revolution, particularly its initial outbreak in Huguang, should not be seen as the result of an outside conspiracy by reform-minded elites like Sun Yat-Sen and Wang Jingwei, but rather initially as the confluence of the anti-Qing sentiments of many social groups at once, but then rapidly subordinated to elite leadership, both conservative and reformist. Indeed, the Wuchang Uprising occurred when Sun's Tongmenghui was undergoing a major schism, and Sun ultimately only managed to hijack anti-Qing uprisings on the Nanjing-Shanghai axis in 1911, with the uprisings in Guangdong being mostly independent and the core revolutionary forces in Huguang being under the control of Qing turncoat Li Yuanhong. Meanwhile, the radical students and rural farmers who initially started the revolt were found very expendable to the elite – student battalions were almost invariably sent in as forlorn hope units by semi-moderate elite leaders so as to dilute radical influences, whilst Jiao Dafeng, the radical leader of the uprising in Hunan, was publicly assassinated by gentry moderates after barely 10 days in power. This is important, as it reminds us that, even beyond geographical divides (which will be outside the scope of this answer) Qing China was not socially united, either, and different classes had their own distinct aims and objectives.
But I've staved off the question long enough. When did the fall of the Qing become inevitable? This is not an easily answered question, nor one with a single answer. As such, rather than simply push one perspective I will instead present a series of candidates for the point of no return and the ways in which they might have been so, and leave it up to the reader somewhat to, depending on their priorities, ponder what the most reasonable point should be. In terms of what to look for in doing so, we must keep in mind that although the Xinhai Revolution was in the end the victory of the elite, this was neither inevitable nor, as noted earlier, the result of an absence of popular support, at least during the outbreak. As such we should not only be considering issues that led to increased dissatisfaction with the Qing more broadly (which were to some extent prominent), but also discerning between those which empowered the elite at the expense of the imperial office and those which emboldened the general public to revolt against it.