Practically speaking even the "non-custodial mobile wallets" are not really wallets, as @npub1ey6qdmvzcgcsr883m9nspzz0mm037l26xtardzcskfsvc6gc7jssm9szvp of Breez highlights in https://medium.com/breez-technology/there-is-no-such-thing-as-a-lightning-wallet-dc9ac46d32

The 3 hardest things in our business are:

1. Naming

2. Off-by-one errors