@AesAthena You can select the layer like an object and use the opacity field in the status bar or in the Fill&Stroke dialog.
This is explained in the release notes:
https://media.inkscape.org/media/doc/release_notes/1.2/Inkscape_1.2.html#Layers_and_Objects_dialog

Some changes to the dialog have been in progress, I've not followed up closely lately. You can try a development version and give feedback on our bug tracker.

@doctormo will probably be able to help you find which version exactly to test.