After upgrade (clean install TBH) I have similar problem setting up Wifi as it was during 26.1:
https://forum.opnsense.org/index.php?topic=50561.msg259285#msg259285
For one machine (UEFI, vga install) everything works OK, but for one older box (non-UEFI BIOS, I had to flash nano install due GPT USB key not booting) ath0 can be created only in BBS Infrastructure Mode and Wifi AP can not be created. In 26.1 times it was solved by hotfix (see link above) and later with 26.1.2