As per subject on linux are there some cmd line switches that allow breaking out of single app instance pattern?

look at https://darkmx.app/run_mode

Put the darkmx executable into it's own folder with darkmx_local_instance_check.txt (empty text file) and when it starts up it will be single-instance but only from that specific folder.  Make another folder the same way, and it can run in a separate instance.  The config files will be stored in the folder with the executable, so your two instances will have completely separate configs, user name, etc.

Consider the use case. One want two profiles to separate activities. The app is updated throgh system regular update routine. Only default configuration up to date. To prevent several big copies of the executable and keeping them up to date, wouldn't be much better the approach of command line parameters where you can tell either an alternative config file or directory to run, plus also optional switches that could be added as outlined on the page.

The dev seems to be afraid of command line switches, Tixati mostly had local .txt files too :-P
Are you sure that the local files don't work as you want them to? I'm pretty sure that "same folder that contains the program" is actually describing the current working directory aka `pwd`. You still get to run the up-to-date system executable but with local data.

looks like it's now added for linux: https://darkmx.app/config_path

I'm pretty sure on linux it is reading the path of the running program from /proc.  Not current working directory.  You can confirm by starting it via a relative path on the command line.  This might be different on the other platforms.