Catalina and old application compatibility regarding new file system access rights I am trying to make Time Lapse Assembler work on Catalina but no luck so far. I can open the UI and input files etc but when it comes to writing a destination file it gives an error without giving much explanation. 

My guess is that it has something to do with Catalina's increased per operation access rights but I am not sure. 

I tried to give write access to Time Lapse Assembler on ~/Downloads, I tried to write on a SD card, tried to create a file with (chmod 777) everybody but no luck either. 

I wonder if there is a trick to explicitly disable checks or if there is any other trick to make Time Lapse Assembler work on Catalina. 

Exact error message on the pop up dialog is: "Error encoding file: There was an error accessing the destination file. File may already exist and be opened in another application. Close other applications and try again.
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.