There's a setting you can click that will remind you (not force you, you can still post without) to add alt text to any images. I find it incredibly helpful.
My instance doesn't use regular Maastodon, so it may look slightly different in yours. But click the hamburger up in the corner to get to settings, and it's in there, somewhere. I was browsing through all of them and found it.
@ScottSoCal could you please let me know how to do that?