As of version 1.4.5 released Jan 27 the game appears to be native Arm. Someone made this: https://forums.terraria.org/index.php?threads/terraria-on-arm-apple-silicon-macs-finally-optimized-for-1-4-5.146473/ thread on the official Terraria forums to confirm this. I also confirmed this in that thread. I also mentioned that if you were to use Galaxy to open the app it was not native but if you just launched it via the Finder it was. I can't comment on performance passed the Menu but I was getting a constant 60fps at 1080P on my M2 Max Mac Studio with version 1.4.5.3 (The game had 3 quick hot fixes in the 4 days following release.)