Catalina and old application compatibility regarding new file system access rights
Have you tried with, for example, macOS High Sierra? If it works then it's not because of the APFS.

What changed with Catalina is that a part of the file system is mounted as write only.

First of all you can try giving full disk access on privacy and security preference.

If that doesn't help try disabling the SIP from recovery mode with csrutil disable and after reboot try sudo mount -uw /; killall Finder to mount everything as read and write.