unlocked samsung s20 5g incompatible

Hello,

I have a brand new unlocked Samsung s20 5G purchased from samsung.com

SM-G981U1

I'm using the sim card with straight talk and it works great

I'd like to switch to xfinitiy and it says my phone is incompatible (???)

Is this an error on xfinity's part?  It makes no sense to me.  Thanks