There have been TOTP PAM modules for ages (these work on a Linux client and Linux server via e.g. SSH). You can even add YubiKey to PAM. Same for BSD Auth and macOS.
It's abandonware these days and hasn't been updated for years. The iOS app doesn't work anymore and can't use the camera for reading codes.
It's not broken for the 15 or so accounts I use it for.
Reading / using existing codes might work properly, or manually inputting them.
I've sent a note to the maintainers, but there's an open git issue for it. Not sure when their commits will roll to the store.
I'm told by multiple colleagues at redhat that they've raised this with internal support, so it should be sorted eventually. Lots of iphones in redhat and this is the app they officially support for TFA internally.