2020 M1 MBA battery won't charge since 15.2 update

2020 M1 MBA with a healthy (85% battery) having all kinds of problems after Sequoia 15.2 update.

• Updated a couple days ago from Ventura to Sequoia 15.2.
• For 2 days, battery would not charge, computer would not recognize that it's plugged in.
• Tried 2 different sets of chargers & cables at 2 different outlets — no dice.
• Started in Safe Mode — no dice.
• Let it sit in Safe Mode for about 10min — suddenly it's charging.
• Rebooted, still charging fine...
• 

• Came back an hour later, it had gone from 51% to 75%...

• ...and now it's not charging anymore — again...

• Menu Bar icon shows plug icon, and dropdown says...
  • Power source: Power adapter
  • Battery is not charging

• System Settings > Battery says...
• Charging: 73%
  • (Remember: it was 75% a couple minutes ago and hasn't been unplugged)

• System Information says...
  • The battery’s charge is below the warning level: No
  • Fully Charged: No
  • Charging: No
  • State of Charge (%): 73
  • Cycle Count: 81
  • Condition: Normal
  • Maximum Capacity: 85%

• Diagnostic Mode returns two codes that point to a problem with the charging port or charger, but...
  • The problem started immediately after 15.2 update
  • The problem remains regardless of which port or which charger (we have several)
  • So this is either a giant coincidence, or it's really a software problem

• After Diagnostic mode, the computer now also auto-reboots whenever shut down (via Apple Menu or holding power button) — it's basically impossible to shut down, even from Safe Mode
• And after Diagnostic mode, battery is rapidly draining — 10% in an hour — while asleep

Other than wishing for the "good old days" when I could reset the SMC, I'm out of ideas.

Anybody?

[Edited by Moderator]