Honestly best approach is to find some small projects you feel need help. Introduce yourself to the development team and offer time and suggestions. Eventually one will say yes.
But as a visually impaired developer I'll give you a heads up. Most pro non foss ui is freaking awfull for accessibility. The choices made over the last 20 year are just bad. OS is far from perfect. But I find the interfaces generally work way better with enlarged text then anything using modern UI ideals.
So please if you get involved. Remember accessibility is more complex the let voice assist work. Most blind folks have some vision. And rellying on the Systems accessibility options is not enough for us to be able to use software in a competitive way.
OS software using the UIs designers seem to dislike. Is generally more customisable for font sizes and colour options accross different parts of the system. In ways able folks would just never consider. This allows us to actually layout software so we only need magnifiers or text readers for things we individually rarely need to read. But can increase the stuff we do in ways that allow us to work at competitive speeds.
Modern UI design is pecomming less accessible as the software becomes much more complex but developers of ui tools seem to see disability as a 0 or 100% slowing disabled users with some ability down to the point they are unemployable.
Please please try to avoid moving the OS stuff we can use that way as well.

Yeah thanks for the effort. You would be stunned at how many web sites make no effort.
Many modern web sites often fail miserably, especially scripted ones. But mostly because companies just don't care. As you say it is hard work. So when companies outsource that hard work is rarely if ever asked for up front. And the cost to modify existing site is hugew..
But remember if we are talking software. Again all the pro measures are based on 0 or 100% able. So again leave all disabled depending on solutions that slow down workload.
All the laws on the West only require reasonable accomadations. And being less productive is never considered reasonable. Or in anyway a hope for a successful career.
So with so much software moving to Web apps. Those AA standards rarely help beyond making the page usable. If your career depends on performance as almost all do. Most disabled are not able to efficiently use them.