HA is supervised on Intel dedicated machine, NAS is OMV 6 quiet basic setup. No RAID and that kind of stuff, no virtual machines involved on both sides.
I solved my issue, but will describe the cause here for others.
I basically copied the command above with create dir + mount, to shell_command.
Shell command was failing with “error 111”.
Same command in Terminal/SSH add-on was partially successful: folder created, NAS mounted, and contents are visible with “ls” command.
But despite the created folder itself was visible in “Media” menu under “Local Media”, it was empty.
I checked, that it’s actually same dir. I uploaded some photo inthere from Media browser, and checked that photo is visible in Terminal (while NAS is unmounted). It was.
Then I tried to remove folder creation from shell_command, leaving only mount part.
And voila, it worked.
I guess, there’s 2 problems:
No permissions to create folders from shell command.
Some drivers issue, that doesn’t show mounted content, if it was mounted AFTER Media browser initialization.