"Popular" leaves too much room for interpretation imo, they should have defined exactly how many downloads, users, etc. is needed.

I also wonder how easy it is to actually make changes to these wallets. I found Blue pretty easy to propose changes to, but I don't know about the lightning wallet repos. Breez and Phoenix have a decent amount of past contributors but the Muun android repo looks like there are only employees who have been working on it.

#2, #3, #4, #9 (to those who have the expertise), and #10 seem like the best projects to work on for people who are not already integrated into an existing open source community and want to jump in to sponsored Bitcoin development.