Thunderbolt & Ethernet. Nice!
A thunderbolt and an Ethernet port. Nice!

USB-C fits
USB-C cable works as expected.

Ethernet too!
Ethernet too!

But both at the same time... Not happening.
But both at the same time… Not happening.

Apply some sandpaper to one side...
Apply some sandpaper to one side…

...Until the Ethernet dongle is a bit thinner on one side.
…Until the Ethernet dongle is a bit thinner on one side.

Perfect!
Perfect!