If WiFi is greyed out, the issue is unlikely to be antenna related. Antennas will just boost the level of the signal, but WiFi could still be enabled. You're signal would just be crummy.
This is much more likely to be a board level issue. The [[iPhone Will Not Connect to WiFi|iPhone Will Not Connect to WiFi|new_window=true]] page offers some fairly comprehensive troubleshooting steps. But I would focus specifically on the logic board section towards the end since I suspect that's your issue.
I don't recall whether or not the gyroscope/accelerometer are also on the bottom board and no schematics available for iPhone 13 series that I know of. But that issue could also be related.