I also have a Beelink GT1.
I use gxm_q201 but the gxm_q200 works too.
The dtb isn’t the problem for the lan.
In the beelink forum, the following workaround helped and the lan is working for several weeks now:
Shut down the device, pull the power, hdmi and lan cable off. Plug the lan in, then the power cable…wait a minute to boot the system, before plugin the hdmi cable again. Now it should work. I use a static IP in my router using dhcp. Dynamic works also. Static in the device did not work.
It seems, that there is some interference between lan and hdmi connector. Hardware issue, has nothing to do with coreelec.
Hope this will help u too.