I don't have 2FA enabled on my eBay account. I use a unique, complicated password though, and I don't see any suspicious activity on my account, though, apparently eBay saw something wrong. Unfortunately they won't tell me what's wrong, so I can't figure it out or help.
AFAIK eBay doesn't support WebAuthn. I got a set of 3 Yubikeys some months ago (1 for my laptop, 1 for my workstation, 1 for backup in my fire safe) and I wanted to protect my eBay account using them, but eBay only offers me options to add SMS or eBay's mobile app as 2nd factors.