What even are brilliant moves anymore???




I think it is because of the computing power of mobile vs desktop.


Wow, what a great tactic. Good game.
There's 2 answers to your question. 1 covered already is the computing power of the device determines to what depth the analysis is done. It's controlled by time, not depth. So, a faster computer analyzes deeper. Second, Chess.com grades moves on a curve when it decides what is brilliant vs good vs whatever. What it considers great/brilliant depends on your rating. Even mistake vs inaccuracy vs blunder is not the same depending on what your rating is.
While I personally don't like the way it's done, it's really no different than a coach talking to a student and analyzing a game with them. They're going to try to be encouraging to the lower rated player and a move that a 2000 student might get scolded for because they didn't see a problem 10 plies later, they understand that the 500 while making the same move is looking ahead 6 plies and for them this is objectively a great success finding that same less-than-engine-perfect move.

Same thing happens to me using an Android. Also, when I first analyze in the app, and then the browser, (using the same device), my accuracy often changes significantly. Evidently the engine analyzes longer in the browser. The app has a number of glitches, which is surprising given chess.com is touted as the premier chess website.

What version of the app? If is listed as Game Report, it's using a different move classification system.

If your app is showing Game Report, it's using a different move classification system.
Game Review uses a different definition for brilliant, which is a sacrifice that is best or good. The older Game Report does something completely different.

it's really no different than a coach talking to a student and analyzing a game with them.
Well, presumably that was the goal. In practice, however, the chess.com script that interprets Stockfish's analysis ("the Coach") is extraordinarily dumb. Even comparing it to a human is a bad joke. You could train a clever dog to be a better chess teacher than "the Coach".
The only sensible thing is to disregard all that. Never use "Game review", that is just nonsense. Use "Analysis" instead.