Thunderbolt 2 to Ethernet adapter - says 2.5GT/s but limited to 1000base-t??

PCIe Link Speed is the speed of the PCIe bus itself and has nothing to do with the actual ethernet link, which is managed by the ethernet controller that is connected via PCIe.

As to why the ethernet link itself is only 1 Gb/s, it could be you need the proper drivers for your add on device.

What is the link to the product page of the adapter that you have?? I could only find the Gigabit ethernet adapter for Thunderbolt2.

Also, internet speed tests are not always a reliable measure of network speeds since they can be affected my a myriad of things external to your home or business.

The old Apple made Ethernet dongle is not rated for high speeds, and has never been updated. You would need a 3rd party Ethernet adapter.

From Apple's published specs, it appear that starting with the 2018 Minis, you could up-spec to 10GB ethernet at time of ordering, but the standard ethernet port was 1GB:

Mac mini (2018) - Technical Specifications

Mac mini (M1, 2020) - Technical specifications

An adapter cannot make a port faster.

amybarnes_usa wrote:

The one I have that is third party is USB-C to Ethernet. I'll have to find a way to get a USB-C female to Thunderbolt 2 male converter to try this third party dongle device.

Thanks for getting me the answer.

😓

Thunderbolt 2 is not compatible with USB. You will need a Thunderbolt2 dock (if you can still find one) in order to use a USB device with a USB-C connector. A simple adapter will not work.