Ok I spent a while trying to figure out how to ask this question of your system, but could you give me the contents of /var/log/installer/casper-md5check.json?
This is all I have in the /var/log/installer folder:
erome@K-39:~$ ls -la /var/log/installer/
total 1160
drwxr-xr-x 2 root root 4096 Jun 12 2020
drwxrwxr-x 12 root syslog 4096 Jan 26 11:03 …
-rw------- 1 root root 1650 Jun 12 2020 casper.log
-rw------- 1 root root 591983 Jun 12 2020 debug
-rw-r–r-- 1 root root 392536 Jun 12 2020 initial-status.gz
-rw-r–r-- 1 root root 58 Jun 12 2020 media-info
-rw------- 1 root root 183727 Jun 12 2020 syslog
There are some news. I uninstalled/ reinstalled libfm-qt and pcmanfm-qt as you suggested.
When I open the file manager for the first time, I still cannot move files ( I have this little red icon that pops up). Then if I open/ close the destination folder, all is fine.
I also created a new user. When logged with this new user, I have no issue.