Sorry for a reply not very useful (got my support ! ;-) ).
I had issues with 20.x and image uploading but didn’t really investigate as I moved to 21.x a few days later (and 20.x is done for me).
May be you should try to jump... ?
I would stick with php7.2 (look to me more tested than the others).
Do you use elfinder ?
If yes try without elfinder just to check.
Also CRSF errors were getting in the way when I had issues (20.x) I think disabled in the Admin => Security to test.