Some users have recently had their accounts hijacked. It seems that the now defunct EVGA forums might have compromised your password there and seems many are using the same PW here. We would suggest you UPDATE YOUR PASSWORD and TURN ON 2FA for your account here to further secure it. None of the compromised accounts had 2FA turned on.
Once you have enabled 2FA, your account will be updated soon to show a badge, letting other members know that you use 2FA to protect your account. This should be beneficial for everyone that uses FSFT.
The Gigabyte B760I Aorus Pro DDR4 exists but I have no experience with this one. Micro Center here still has 3 in stock but they are 209.99.. Kind of steep but maybe not if you have everything else?
B760 mATX is still relatively affordable and available brand new to avoid any used mobo issues. LGA1700 ITX DDR4 is like three motherboards ever made, I think.
B760 isn't the greatest fit for a 13900K but I suppose if you're not going to overclock / plan to undervolt to minimize degradation, it's a solid option. Plus Z690 / Z790 DDR4 boards in good condition are hard to find at decent prices (I've been hoarding lol).
If you don't mind Aliexpress, there are several Jginyue brand B760i ITX boards. Unfortunately, they're around $150. I bought one about a year ago and it works perfectly fine, but it was only about $80 back then.