You can check this out to see how apps look on the Librem 5:
I’ll add that there are thousands upon thousands of applications in Linux, available for free download through official software repositories. Not many of these are adapted to work on a mobile interface…yet. But now that real Linux phones are finally being produced, the ecosystem will grow rapidly.
(You can check any of these terms on Wikipedia to get a better explanation than I’ve provided, I’m sure.)