GrapheneOS will not (and will probably never) make a formal recommendation for a cryptocurrency wallet, and considering recent events regarding some popular offerings it is best to leave that responsibility to the users. If a project was endorsed that ended up having consequential events (unmaintained, a breach of trust, legal issues) then that would be terrible. Doing such a move is a dangerous slope. We are grateful wallet developers recommend and use GrapheneOS however.

Use a wallet that is up to date, maintained and trustworthy and follows app security practices. Avoid suspicious apps. If you use a cold wallet then use your official or endorsed by manufacturer apps to avoid as many trusted parties as possible.

However, it is up for recommendation to follow the core cryptocurrency security practices. Use GrapheneOS for funds you are okay with the potential risk of loss if you are using the device as your smartphone. Your phone will not protect your funds for a lifetime, if you are concerned you have been compromised or you no longer have access to the device holding those funds, move the funds to a new address/wallet as soon as possible. The security model for smartphone wallets are that you are expected to move the funds if you lose the device that accesses it.