Hello,
Unfortunately, I think we can do next to nothing against the inaccessibility of these giants.
Whenever they talk and do something about accessibility, it's only to avoid be caught by the law.
When they do something, they do only the bare minimum. They don't do it with care, and they don't actually test with screen reader users if it really works or not.
The result is, sadly, something which is technically accessible, but not practically accessible, and not at all comfortable to use.
Additionally, they exists since 25 years or so, and so have certainly a very long story of awful code, optimized for IE6 and even earlier, almost didn't evolved since then because it's very hard to upgrade a gigantic code base that does almost everything, at a time where accessibility was totally unknown.
Note that, even sighted people often say that such work management apps offer quite poor experience, even HR people.
And they continue to pay a lot for these apps nevertheless, because they have all their data stored in it and because it's also very hard for companies to switch to another product (there also aren't that many available).
At work, we don't use SAP, but another app which is as much unusable and as much a gas factory. I have no other possibility but ask other colleegues or HR to record certain thigs for me.
ON the task/project management app called Jira that we use, there is an accessibility plugin, but it costs a lot, and is far from solving everything.
So well, I ask other people for things that I can't do myself, or when it would take me one hour while it takes 5 minutes for them, and voilà.
Sorry not to bring very positive news.