That is why forks like librewolf exist.
Have you tried switching off the energy saving option
Which nvidia card and what driver version.
Nord theme
Can you try an LTS kernel .
Was there ever a kernel update for you
Have you checked your gdm custom.conf
A music player maybe like clementine
No manjaro never do it
Good to know
Turn off secure boot and just check if anyone has ever run your device with linux before. And kde plasma is a de not a distro.