@dcoistek how did you install MagicMirror? the automated script?
did you say yes to pm2 to autostart at boot?

if so you can use pm2 to run another app

see the help for the pm2 command

pm2 --help

in general, by convention, all linux commands are supposed to have help with
-help of --help

some may also pro ide a manual file
accessible thru the man command

man command_name

man ls
man pm2
etc
q will edit the man viewer.

I think mmpm has a process that needs to be started to work

pm2 start process,_name
pm2 save
will set it up for system at boot

note if the process_nane is a shell script
it needs to be named with the .sh extension, or you gave to launch the shell in the command to pm2

pm2 start bash /c script_file_name