Sublime Text is able to save files to which the current user doesn’t have permissions to save thanks to gksu - unfortunately, gksu itself is deprecated and removed from newer Linux distributions. A replacement based on PolicyKit, pkexec, provides similar capabilities in newer (Ubuntu 18.04+, CentOS/RHEL 8+, etc). Could you consider replacing gksu support with pkexec?
So it seems like everything should work without gksu…
Oh, well then, it seems like something must be wrong on my end. Thanks!