Surface pro 8 type cover not connecting

This is something that has been intermittent with this machine since I got it -- as has been the intermittent Windows Hello face recognition. However, they work more than not, and a restart usually solves it. As long as they would work after a restart, I accepted this as small niggle I'd put up with. Yesterday, the type cover again disconnected, but this time none of the usual fixes worked. I noticed there were some updates available, so installed those, and the keyboard was again connected after the restart, the key backlights worked, as did the trackpad/cursor. However it was gone after the next restart, and nothing is working to reconnect it. I tried ALL the methods from the MS help for this problem. (hard reset, etc) I then updated to 26h2. Nothing. For my purposes, the tablet is close to useless without a working type cover.

Troubleshooting Attempted
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• Several combinations of force reboots (with power attached/not attached, with keyboard attached, not attached)
  Including holding power for 20 seconds on restart
• Updated to 26h2 build 26300 9457
  (Note: I updated *after* discovering the issue)
• Checked UEFI (no Devices menu)
• I ran Surface Diagnostic Tool and it said it couldn't check the keyboard because it didn't test third-party equipment, but it is in fact a MSFT-branded keyboard.

Thoughts? Suggestions.