Hi friends!
I have this adapter: 2.5GbE USB C to Ethernet Adapter:
www.startech.com
I installed the Realtek RTL 8153 driver "RTUNICv1.0.20.dmg" from the website.
And I plugged it into my Big Sur machine
But there is no 2500base option in the network settings.
It's limited to 100basetT.
Does anybody have any idea?
I have this adapter: 2.5GbE USB C to Ethernet Adapter:

2.5GbE USB C to Ethernet Adapter NBASE-T NIC - USB 3.0 Type C 2.5/1 Gigabit/100 Mbps Multi Speed Net
Add a 2.5Gb Ethernet port to your MacBook, Chromebook or laptop with USB-C or Thunderbolt 3

I installed the Realtek RTL 8153 driver "RTUNICv1.0.20.dmg" from the website.
And I plugged it into my Big Sur machine
But there is no 2500base option in the network settings.
It's limited to 100basetT.
Does anybody have any idea?