Pathbuilder doesn't support Starfinder 2E yet, but the developer is working on that per his Patreon posts ( https://www.patreon.com/c/redrazors/posts ).
Similarly, the app version isn't generally available yet on iOS (there was a test build for backers), but he's submitted to Apple and gone through a few submit / rejection-feedback cycles so far so hopefully it won't be much longer.
Don't know how well FoundryVTT works on mobile browsers as I've never used that VTT, but I vaguely recall reading that it's not a great experience since the standard UI isn't designed for touch. The VTT that I do use (Fantasy Grounds) has been working on a reader application so that people will at least be able to read reference material on a tablet, but there's no ETA.
