How to make everything selectable? I made a lot of objects unselectable (intentionally). Now, instead of un-clicking them one by one in the outliner I'd like a button like make all objects selectable. Can a Python script do that?
You can for scene objects:
import bpy

for obj in bpy.context.scene.collection.all_objects:
    obj.hide_select = False

Or for all objects in the file:
import bpy

for obj in bpy.data.objects:
    obj.hide_select = False