Tips
1. Make desktop mode permanent
to boot into desktop mode by default
steamos-session-select plasma-persistent
to boot into gaming mode by default (and to fix inability to go back to gaming mode from desktop)
steamos-session-select gamescope
2. Turn off readonly mode
Run the following command to disable readonly mode so that you can install packages via pacman or yay
sudo steamos-readonly disable
Run the following command to re-enable readonly mode
sudo steamos-readonly enable