For those that cannot get discord notifications on their phones, and uses a paid DNS like NextDNS.

I have had this problem for the last 10 months on my s24 ultra, no notifications for discord.  Yet my sister was getting notifications on her samsung A05  for discord.

Today I found the problem.  

You need to unblock:
 

*.firebase.google.com

After that you will get notifications when the app on your PC is close.  I been testing this for the last 5 minutes and wanted to share it, incase someone else is having this problem too.