⭐ Merited by dkbit98 (1)
As of right now, honestly nothing. I will look into something simple, without tons of bloat introduced by suspicious (read: Google et. al) frameworks that I can compile myself, in the future.
That would be cool to see 
I am currently thinking about all the good apps we can use for smartphones, related with Bitcoin, and open source wallets are big part of this.
This is not to be used for holding big amount's of money, more like pocket money and something used for p2p trading in person.
One interesting thing I noticed recently is that Graphene OS with Pixel6 phone is using twelve words backup option and I think this could be BIP39 compatible but I am not sure.
https://walletscrutiny.com/?verdict=reproducible&platform=android
As for iOS, as far as I know it is impossible to make a reproducible build land on the AppStore, since Apple re-builds the binaries themselves or something like that. But you could surely compile one of the open-source iOS apps yourself.
https://walletscrutiny.com/?verdict=nonverifiable&platform=iphone
However I don't know which ones support airgapped hardware wallets in either list. As I said, for very basic functionality, I may be able to throw something together in a weekend. But as of right now, I don't really have a need for it. I did plan to have one hardware wallet more intended for 'mobile use' (at first I thought Passport v1, then I decided to give that role to my batch 2 due to the battery issue), but especially with the still ongoing pandemic I just don't travel that much or use Bitcoin outside 'range' of a PC or laptop.