Just to clarify. You installed 20 and it came with MIUI compass installed? If you installed it after then I have no idea if it will help at all. I was hoping for a built-in compass app.
Have you tried to change preferred network type in settings? This happened to me after the instal, the preferred netwotk type was set to: LTE, TD-SCDMA , CDMA,... I changed it to : WORLD and the 5G appeared immediately.
You mean 'Global' and not World?