Explanation:
You have a hybrid system and you are plugging your external monitor into the nvidia dGPU.
So when you have it set to hybrid mode (AMD on, Nvidia off until called) then it wont work.
Arguably one of the easier methods for dealing with this is simply setting everything on the nvidia.
This can be achieved most preferably but only in rare cases through a BIOS option.
But as that is uncommon another approach is using a utility like envycontrol as shown in the post above.
You can also avoid the use of such utilities through ‘reverse prime’, but this is somewhat involved.
https://wiki.archlinux.org/title/PRIME#Discrete_card_as_primary_GPU