So I just came over from reddit and I figure this would be a good place to accumulate some experiences with screen reader navigation on lemmy.
I myself use orca on arch linux. The site seems usable so far. Posts are level 5 headings, and though I wish they would have used the paragraph tag for navigating posts with p, I can use o to jump to large objects, which will read out posts.
The biggest problem I encountered so far was during community creation, where the language multi-select list did not indicate which languages were selected/deselected. Still trying to figure this out atm, as the edit community button also doesn't seem to be selectable with keyboard. This problem seems to repeat when making a post.
Selecting a community when making a post is also a little tricky. I was able to do it by clicking (with numpad) on 'Community', which opens a combo box with a list of many communities. I then hat to hit 'tab', orca will say 'Combo box collapsed', and I could type in 'blind'. The list of selections then changed to a list with only 2 options, this one and one other. Selecting 'blind' with the arrow keys and hitting enter selected the 'blind' community successfully. I think this could be much improved.
Anyways, I'll probably edit the post when more comes up. Would be glad to hear other's experiences. Both problems and workarounds.