What can a school wifi certificate see?

Had to download a certificate for the school wifi on my laptop what can they see?

I had to import the file to Firefox

I know they can see unencrypted message, can they see ones that were sent out before i went on the wifi, can they see my friends messages (specifically discord)

Can they see me opening offline software like krita

If an offline app needs an launcher (for example steam) can they see the app opened or just the launcher?

Is there any potential risk of them seeing my stuff when connected to my home wifi