I have a 10gbe server connected to a 2018 mac mini with a 2.5gb usbc adapter (through an unmanaged switch). I am wondering if there is a way to use both it AND the 1gb ethernet to get a higher throughput?
No.
Teaming NICs doesn’t make a bigger pipe. It makes a « larger » pipe to the server. This one will be able to handle more requests, not making each one faster.
Mac mini must have a 10gbps ethernet NIC to be able to transfer faster from server. If there is a switch in between them this switch must also be 10 gbps.