Re the broken chain, I was thinking this is also a pretty old cassette, dating from my 2018 MTB, with plenty of miles before moving to my commuter in 2022. Putting a new chain on it when the last one got so bad, feels iffy. And I was starting to regret the total in the shopping cart. Then I remembered I have a nearly complete and nearly unused SLX 11 speed drivetrain installed on my tandem. I had been intending to remove it anyhow and return the tandem to original 3x8, as it never gets ridden and needs the kidback removed. See if the kids will ride it with crank shorteners, or I just donate it. So that all can move to the commuter, four pieces (cassette RD shifter chain). Assuming the chain is long enough. It should be similar. And all it will take is a massive amount of work.

I could also steal the chain from my 2023 MTB build that has not been used much at all either. That does not feel as likely, though. That bike still has a future even if it doesn't have much of a present