@fossfreedom there’s had some ( welcome ) changes in trash-applet behaviour since first post here.
These days on 20.04 I noticed some folders can’t be deleted using trash-applet but files are deleted as expected.
Those files and folders came from my ~/Desktop and this ~/Desktop is actually a symlink to /media/DATA/user1000/Desktop on another disk’s partition. A .Trash-1000 folder sits in the root of that partition, belonging to 1000
I can delete those folders using trash in Nemo.
So does not look like a rights/permissions issue, maybe something about file « types » ?