Some of this is dated now, but check out: List of Apps that fit and function well [Post them here.]
And: Tips & Tricks · Wiki · Librem5 / Librem 5 Community Wiki · GitLab
Also, just search the forums for “tutorial” to get an idea of some capabilities you might not expect.
You might also check out @linmob’s site: https://linuxphoneapps.org/
He has experience with both Pinephone and Librem 5.