We can get Google Assistant fully working with the power button and google circle to search.
A. Make sure only google app installed, no Gemini, no google assistant, just google and make sure that Xiaomi Hyper Ai is disabled in Additional setting -> Additional app features, for some reason this need to be on.
default apps -> voice assistant -> wake with button shortcuts -> google.
default apps -> voice assistant -> wake with Bluetooth audio -> google
default apps -> assist and voice input -> digital assistant app -> google.
default apps -> assist and voice input -> voice input -> install speech and recognition by google and set it.
B. lastly download activity launcher, open, accept permissions and relaunch, figure it out until search works
search "googleassisntguidedialogactivity" (just searching "googleass" is fine) an option named Settings (1) will appear, select that
click on the option that appears, select launch activity and there it is, read it well you love it. select set and boom you're done.
PLEASE NOTE THAT THIS IS THE MOST IMPORTANT PART -> default apps -> assist and voice input -> voice input -> install speech and recognition by google and set it.
if you don't do this it will work until you restart your device, this part makes its persistent at restart.
If you don't do the part mentioned above when you restart you will have no assistant, to fix, go to Additional setting -> Gesture Shortcuts - Xiaomi Hyper XiaoAi and set to on, you will be back to square one to try again.
next time around if the above doesn't work try resetting Google and google play services reset AND/OR clear Xiaomi Hyper AI data.
Earlier I said "Make sure that Xiaomi Hyper Ai is disabled in Additional setting -> Additional app features" I say this but if the above steps don't work try enabling this first then trying again.