@Arrakis
Ok, some more approaches...
1) First try one more kext (attached). This one (SmallTreeIntel82576_mod.kext), I'd modified in 2019 (it works with I211 and with I210), adding a 'root' ending to the Info.plist file that was missing from original and would give an occasional panic without.
Also, have you set the following in red box to "Yes" (it might help):
2) Are you injecting a DSDT or SSDT that might be interfering? Specifically, I'm wondering what is inside your "SSDT-EC-USBX-DESKTOP.aml". It is possible that the 'DESKTOP' portion is a DSDT extract that may be giving you grief. Instead of enabling this aml file, disable it and use the one attached below (SSDT-TRX40-USBX.aml).
BTW, if you want to get a summary of all loaded, non-Apple kext files, enter the following into Terminal:
Kextstat | grep -v com.apple
My results are in Spoiler below:
3) The next approach is to create a kext patch. Try the attached code shown in the Spoiler below, if the above SSDT swap does not work.
4) Finally, what about trying to inject AppleIntelI210Ethernet.kext? Attached is one I extracted from the latest Big Sur beta. If you use this, I'd try with and without the SmallTree82576 kext enabled, listing the SmallTree after AppleIntelI210Ethernet kext as in Spoiler.
In any of these situations, you can probably still use the Device/Properties stuff I uploaded earlier. In fact, in Comet Lake mobos, AppleIntelI210Ethernet can have a kernel panic that is only resolved with a DeviceProperties injection (see here).
Also, remember to try re-setting NVRAM.
***
If the I210 works, you should see sometime like I see for I211:
SDDT-TRX40-USBX.aml.zipSmallTreeIntel82576_mod.kext.zip
AppleIntelI210Ethernet.kext.zip