The Linux version, in a container no less, handles the entire gigabit bandwidth.

And let's be clear, it wasn't the app that had problems, the Apple Remote Desktop connection to the machine failed when the speeds got above 40MB/s and the network interface stopped working around 80MB/s.

I think Transmission works perfectly fine. I've been using it for 10+ years with no issues at all on Linux.

I forgot to mention this is a Mac mini/Intel (2018).