Test results with LineageOS 20 are very promising. Flashing worked without issues. I just followed their instructions. I didn’t flash GApps.
Pretty much everything I tested works absolutely flawlessly so far, including WiFi, Calls, SMS, Bluetooth, Flashlight, Dual SIM and Camera.
The only issue I was able to find is that in light UI mode a few icons on the bottom right corner of the keyboard are occasionally invisible, but that’s really a minor problem. So far I have also not succeeded in registering Signal; the verification SMS step is a bit temperamental as always (didn’t spend too much time on it though).
The responsiveness of the device is nothing short of phenomenal, especially compared to stock MIUI. The lack of bloatware makes the system very usable even with the meager 32 GB of internal storage.
In summary, highly recommended until we have /e/ for this model.