The most flawless versions are from B-S-G, which are named like "MGC_6.1.021_MI8_V2b.apk", many developers use B-S-G versions as a base and add more features or compabilities. B-S-G versions can accessed in a telegram channel.
GC(Mi8) by B-S-G
Here you can find port GCam specially for Xiaomi Mi 8.
Download telegram and join the channel above, you can find latest version and instructions.
The other versions are not intended to work on mi8, but you can also try it by yourself. In my experience, some of them DO NOT WORK on MIUI roms.
You can download them by the link: https://www.celsoazevedo.com/files/a...google-camera/
For the fresh users of google camera, here are some settings recommended by B-S-G. They are just an basic instructions, if you have higher demands it is better to change the settings by yourself.