How to invoke a command when starting a user session?

OS: Ubuntu 22.10
graphic card: nvidia
monitor: philips

Issue: how to change default gamma after X11 startup.

The gamma command I wish to invoke is either:

xgamma -rgamma 0.6 -ggamma 0.5 -bgamma 0.5

or

xrandr --output DP-0 --gamma 0.6:0.5:0.5

I want to set the gamma to default per above, when my user session starts.

I have attempted:

1. To invoke a .sh file at startup by adding an entry to the "Startup Applications". This is unsuccessful: the .sh will not invoke. Adding a 10 second delay does nothing.
2. Editing the file, xinitrc, to add the xgamma or xrandr commands. Also unsuccessful.
3. Creating a .conf file in user/share/X11/xorg.conf.d Also unsuccessful. This caused my pc not to boot, requiring a recovery session as root, to remove the .conf file.
4. Creating an .sh file on desktop, and invoking after user session starts. Successful, partly. But this is not default, and the system will over-ride the .sh command upon sleep and invoking other applications. Not the solution I am hoping to achieve.

Any help is sincerely appreciated. Thank you.

Update #1:

As suggested in the comments, I ran this command as a startup application:

sh -c '{ echo "started"; xgamma -rgamma 0.6 -ggamma 0.5 -bgamma 0.5; echo "$?"; echo "ended"; } > /home/user/startupapp.log 2>&1'

Here are the contents of the logs from cat ~/startupapp.log... for the xgamma command:

started
-> Red 1.000, Green 1.000, Blue 1.000 
<- Red 0.600, Green 0.500, Blue 0.500 
0 
ended

And for the xrandr command:

started
0
ended

After invoking the xgamma command, though the log shows the change in gamma, the monitor remains at gamma values 1.00.