Before the release of iOS 13, Joy and I used a shared Apple Reminders list called “Grocery” to keep our grocery list in.
I've found the Reminders app to be completely broken for me now in iOS 13. I can't get my phone, ipad, and icloud.com to agree on which lists I have.
Apple has explicitly stated sharing a list is broken in iOS 13:
Sharing a Reminders list using the Add People function does not work currently in iOS 13. Apple is aware of this issue, and it will be resolved in a future software update.
That support article was published November 12, 2019! As of this writing, there's no fix coming even in the newest iOS 13.4 beta.
Now I have to bug Joy to add items to the grocery list on her phone.