There has been a substantial amount of research done on modern veterans with hearing loss, which occurs to about 7.5% of combat-deployed soldiers in the 21st century. The Department of Veterans Affairs pays out about US $1b annually to veterans listed as disabled due to hearing loss.

But you asked about the 19th and 20th centuries, and there's far less data on that. Prior to the Civil War, deafness was a family problem and deaf people were commonly cared for at home and by their communities - but combat-deafened veterans who could no longer work were seen as freeloaders trying to get money from the government, even though society just wasn't set up for a whole bunch of new deaf workers.

Some 33% of Civil War veterans receiving pensions were receiving them due to hearing loss, the number being so high because hearing protection for soldiers wasn't really a thing until 1944. Prior to that, society commonly believed that you could build up a "tolerance" to noise, and then you wouldn't have hearing loss; if you shied away from noise and tried to protect yourself, you were seen as weak.

So soldiers lost their hearing because guns are loud and you're weak if you try to protect yourself, and then they got stigmatized as freeloaders when they received government money for their hearing loss. Not a great environment in which to look for a job. Add to that the fact that there's no governmental protections for getting a job, and the increased industralization during this time, and getting a job is hard. It's much easier in the cottage industry, but everybody's working in factories now, and so most veterans end up living off their pensions instead. Audiometry wasn't advanced at this stage, so we have no data on how much hearing loss most of them had - it is likely that most of them struggled with communication, but we can't tell if they were severely deaf, profoundly deaf, or anything else - we only know that a great many of them were disabled enough to draw pensions.

The result is that while a great many soldiers in the Civil War and WWI did return home with hearing loss, there wasn't that great an impact on civilian life or the workforce. Most of these men simply didn't return to the workforce; they were seen as weak and a drain on society by their local communities and the nation at large.

A caveat on this data: it is possible that even more soldiers had minimal enough hearing loss that they did not seek government support. Because we can only measure those soldiers who applied for pensions, not those who went home and went about their lives mildly hard of hearing, we can only understand a fraction of the entire picture.

Additional reading:

Wells, Timothy S et al. “Hearing loss associated with US military combat deployment.” Noise & health vol. 17,74 (2015): 34-42. doi:10.4103/1463-1741.149574

Sewell, R. K., Song, C. , Bauman, N. M., Smith, R. J. and Blanck, P. (2004), Hearing Loss in Union Army Veterans from 1862 to 1920. The Laryngoscope, 114: 2147-2153. doi:10.1097/01.mlg.0000149448.60511.22

McIlwain, D. S., Gates, K., & Ciliax, D. (2008). Heritage of army audiology and the road ahead: the Army Hearing Program. American journal of public health, 98(12), 2167–2172. doi:10.2105/AJPH.2007.128504

Hill, Corrina S. (2014). The social integration of Civil War veterans with hearing loss: the roles of government and media. Thesis.