I've just had a different experience. Thunderbolt3 is solidly built into the Linux kernel. Nvidia's implementations are also better than ever before. So it's definitely not due to a lack of drivers.
The Razer Core GPU appears directly after connecting with lspci.
I just had a little trouble with the configuration of Xorg (Wayland doesn't run at all).
In Xorg, the option AllowExternalGpus is important.
Only those who think they will get Plug'N'Play under Linux will be disappointed. Switch XORG Config for EGPU, reboot device with attached eGPU. Switch XORG Config back to Intrne GPU's, restart without eGPU.
I then used this:
https://github.com/hertg...
This checks on booting via Systemd Service whether a device is attached and creates the respective symlink to the corresponding config. With this, you still have to reboot, but you don't have to move/symbolise conifgs by hand.
For me, it runs on Fedora Silverblue 31, but I don't see any problems with Ubuntu either.
Greetings
