In EU/UK, some are sadly app only. I avoid those. Many others are pushing apps as a 2FA, even if you use their website. You need to insist to get another authentication system, like TAN. Some governments are also pushing mobile IDs.

The best Linux for phones, SailfishOS, has a fairly good Android compatibility layer that runs many bank apps well. But despite that, it's an uphill battle. The network effect of the duopoly is gigantic.