Hello!
I first noticed the problem when joining a friend's world. My hotbar is invisible but still usable. Name tags above players' heads are missing, and I am not getting chat notifications that would normally appear in the top left corner of my screen. I have the same issue whether I'm on a server, or in my own worlds. I've tried restarting Minecraft, and my PC multiple times.
Thanks in advance for any help!
Can you confirm that the toggle to hide the HUD hasn't been enabled? Settings → Video → Hide HUD.
If this setting is enabled, then it is working as intended. If you did not intentionally enable this setting, that may be a related, but separate, issue