There isn’t a good comprehensive list. Not only that, but I think the specifics are slightly different for MT, DT, and Public Cloud.
Off the top of my head:
BPM’s: No code, blocks only.
RDD Reports: I haven’t noticed anything, besides testing being tedious. They did a little to help that but still more steps than on prem.
Customizations: Nothing limited that I know of. Can use local c# code.
Menu Maintenance: No constraints here that I know of, but I don’t have rights to menu maintaince myself so not 100% sure.
BAQs: No external BAQ’s, views, or anything that would require server access. Updatable BAQ’s work fine but I think I had to take a class before they would let me use them.
Dashboards: No limitations as far as I know.
Data Fixes: Pretty sure Epicor has to run these.