I can’t pair my Apple Watch to my new IPhone 13

If this is a watch you had paired to a previous phone, did you unpair it from the previous phone before you set up the new phone? If no, the watch is still paired to the previous phone and must be either removed from that phone or completely erased in order to pair with the new phone.

See this link --> Unpair and erase your Apple Watch - Apple Support - see the section on if you don't have your previous iPhone if that applies to you.

Once removed or erased, you can then set it up with your new phone.