I was running Lubuntu on a decently reliable PNY USB stick, but I would probably advise against this because my filesystem corrupted itself and I've since been wayyyy too lazy to reinstall and reformat everything.
I'm not a programmer by trade so I just use my LG Zone4 to do everything digital in my life currently.
Quick search for Ubuntu Touch seems to suggest Canonical stopped working on it and it's now maintained by the community.
I like my T420 a lot, especially the build, keyboard, screen, general familiarity. I've used it for 7 years (i7, replaced the original HDD with an SDD a while ago, replaced the battery too).
But a T420 is far different than a tablet with a touchscreen that weighs a few hundred grams.
Currently the only one that fits that bill is Dell XPS13 and that comes with just one flavor (Ubuntu). Most laptops will have random driver issues or another.
I think it’s crazy how bad the laptop market is these days. If you’re barred from Lenovo then you only have two high quality options, MacBooks and surface books and neither run Linux out of the box.
I wanted one too, but eventually I gave up and settled in the apple ecosystem.