I'm very experienced with desktop Linux, and I recently installed PostmarketOS on an older phone. It and Ubuntu Touch are derived from traditional desktop Linux and have the potential to run the same apps.

It's not there yet for people asking questions like the ones you are. I wouldn't even say it's there yet for people like me as a primary phone. The set of apps designed for mobile is minimal and not necessarily feature-complete. Hardware support is partial on most supported phones. Apps not specifically designed for a phone screen are not a good experience at all. Sometimes parts of the OS crash.

LineageOS, on the other hand is Android. It's designed for phones, and it will work pretty much like the Android your phone came with. It does not come with Google apps and services by default, which reduces the selection of third-party apps that work out of the box. You can add MicroG for an open source implementation of most of those Google services, which will make most third-party apps work while still keeping your phone Google-free.