So, I made an armature for my bipedal model and successfully rigged it in Blender 2.7. Since then, I updated to 2.9, and then added some Mouth bones to my armature. Now I want to weight paint my model to the Mouth bones, but I'm unable to select bones in the armature. I cannot click it!
Link to my .blend file: https://drive.google.com/file/d/1XkwYgJpSaftngevlgV5yr7aEJITty4LG/view?usp=sharing
Thank you for any answers and comments. :)