Is it just not highlighting so it looks like you can't select it?
It's as if the face does not exist. If I click on it nothing gets selected or highlighted. I think sometimes when this happens I am able to select it it just doesn't get highlighted in blue but I can't confirm.
I can click on the face and then hit delete and nothing happens.
If you press Ctrl+N to enable component colours does it highlight better?
Command + N opens a new file, control + N does nothing. I'm assuming you're talking about color coding components outlined here?:
https://help.autodesk.com/view/fusion360/ENU/?guid=GUID-4969CAA2-5C5F-4E84-B046-92EB480D5024
When you click and hold there are 2 faces to select, the bottom selection if a back face, what is selected if you choose the top selection in on the menu?
Idk, can't test that now. It's working now:

If it's not selectable at all does a restart of Fusion help?
I've experienced this since the last major update. Many restarts in between.
- Time Magazine’s Person of the Year 2006
- Apple M1 Max rMBP A2485 // Latest MacOS // Latest Fusion
- Usually working off files uploaded to Fusion as: Step, STL, SLDPRT. If it matters ask me.