It's a new-ish project FYI. But to answer your questions:
- Apps: It's Linux (like desktop or server), but "image-based" so you install apps in containers like iOS or Android do (and therefore OS updates basically-never break). https://flathub.org is generally the main app store for Linux containerized phone apps.
Nitpick regarding apps: https://flathub.org/en/apps/collection/mobile/1 is the better link IMHO, even if not all apps in it do actually perform great on mobile [0], and some apps that work well on Mobile are not part of the collection due to lacking some bits in app metadata [1]. Help with sorting this out is very much welcome :-)
- Apps: It's Linux (like desktop or server), but "image-based" so you install apps in containers like iOS or Android do (and therefore OS updates basically-never break). https://flathub.org is generally the main app store for Linux containerized phone apps.
- Screenshots: It'll look the same as other Linux-on-phones, so like https://en.wikipedia.org/wiki/PostmarketOS for instance. It's just built differently.