Solved. I installed Mi Fitness in another profile with google play store, get the logs to get the authkey, uninstalled Mi Fitness, switched to my regular profile, installed Mi Fitness via Aurora Store, paired the Mi Band, installed GadgetBridge.
Then analyses the logs to find the authkey, linked to GadgetBridge, enter the authkey, et voilĂ , MiBand 7 appaired to GadgetBridge. Then unisntalled the Mi Fitness app.