undervolted my rx 9070 xt and fps went up, is that normal?

yeah. RDNA cards like undervolts. just test with the games you actually play. one game can be stable at a value another one crashes on, so if anything crashes later, try a less aggressive undervolt before blaming the game.

Yep, that's normal. The card boosts as high as power and temperature allow, so lowering voltage means it hits those limits later and holds higher clocks for longer. Run a few hours of an actual game to check it's stable though, benchmarks pass undervolts that a real game will crash on.