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.

Well, it's android so it has a much better app support, better UI, it's more stable and it's more familiar than Linux on phones

LineageOs is basically android without google. You can install the google stuff if you want it, or use open source alternatives like microg. F-droid replaces Google play. It gives you access to all the open source apps that do the stuff you do.

Ubuntu touch is more of a full Linux distro that has been optimized for a phone. It works. Mostly things function, but it is limited. Not a lot of support for mobile type apps.

I've used both on a few phones. I daily use lineages. I don't think Ubuntu is ready for daily use yet. I think with lineages, you could install it get it set up in a few hours. Take a week to find apps to replace the ones your used to. And you would not really notice that your on lineageOS.

My recommendations is to just install f-droid now and start using open source apps instead of whatever you are using. Slowly eliminate all the apps from google play. Take a month to see if you can live without google. If you can, switch to lineageOS. If not, at least you learned something.