My wife and I use SimpleNote. I know it’s not a proper grocery app but it works really well. One person can create the grocery list initially then share with another. Either of us can then add to the list if we think of things we need or tick the box if we have bought it. Instantly updated on each others tablets, phone, desktop automatically. It’s free too!
Well done. I have been having similar port forwarding problems as you. Had started to look at cloudflare tunnels but am now encouraged to go ahead. Thanks