There’s a lot to unpack here. In no particular order.
You don’t need cat 8 for 10G. Cat 8 is for 25G - 40G. You can reliably run 10G over
cat 6 cable (I do) at it’s rated distance of 55 meters. I have also been able to cheat
and get a few more feet…
You need a 10G Ethernet adapter to get 10G Ethernet. The Thunderbolt ports are
external interfaces to your internal PCI bus. You have to plug something in to them.
Yes, you can network 2 Thunderbolt ports together. You can also use speaker wire
and connect 2 serial ports together. This does not provide a routable network
The Microtik switch you referenced has SFP+ ports, this is FIBER. If you want
copper ports (Cat 6, 7) then you are looking for a 10GBASE-T interface on your
10G switch. Looks like the QNAP either has, or will accommodate a 10GBASE-T
adapter. In which case, the Microtik switch has the “wrong” ports for you, unless
you want to include a fiber media converter box (10GBASE-T to SFP+)
Don’t do it. Take a look at your distances and use cat 6 and 10GBASE-T
There do appear to be adapters for TB to 10GB ethernet:
It would appear that this is an expensive proposition, but if you have need for that speed of networking…
If your sole purpose is sharing files to one computer, you could do TB to TB between the Mac mini and one other machine, but to my knowledge there is no way to “hub” TB connections as you can for ethernet, so TB networking is point to point. I would expect you could use the Mini as a gateway for any other computer connected to it.
Depending on your needs, you might be better off just connecting via these Thunderbolt to 10GB ethernet bridges to the switch you referenced. Your outgoing connection from your house is probably not more than 1GB, so you can uplink from the switch to your router.