@DeniGu Aha! I think this is on to something.
When I have both my phone and laptop available I usually read email on my laptop, so most of my prior attempts were likely on my laptop.
We’ve recently tried to share 2 new lists. When I clicked the first one in the Gmail app on my phone, I got
which I suspect is the phone equivalent of the “Can’t find list” error. But when I clicked on the other list, I got this screen which I’d never seen before (redacted)
and clicking “Become an editor” led to a window with a Join button
and clicking that led me to a new version of the shared list with “Add”, “Share” and “Leave” options.
Thanks! It looks like this finally worked!
Since neither the sharer’s nor recipient’s message seems to indicate the email link must be clicked on the phone, and clicking on a computer adds the read-only version to Maps on both the computer and phone instead of a warning or error message, I hadn’t thought to try that permutation. I don’t recall any of the documentation mentioning this, either. Or did I somehow miss some clear indication that it’s only supposed to work when clicking on a phone?
With this new understanding I expect we’ll be able to get the other list to work, too. Thanks again!