@tomini nothing is bricked!! don't worry. You just need to do the correct steps.
1) Uninstall Mi fit (DO NOT UNPAIR Mi Band)
2) Install Mi Fit 3.4.4 from Playstore or from the forum that has latest firmware
3) Now open new Mi Fit and check if it will update everything and if after this everything will work
4) In case is not working then you have to do these steps:
5) Unistall Mi Fit and Install 3.4.3 version
6) Install through Gadget Bridge firmware 1.2.0.8 Official English
7) Install though Gadget Bridge Resources v34 for Firmware 1.2.0.8
8) Now Mi Band should work whitout problem
9) Now if you want to update Unistall Mi Fit and Install 3.4.4 and let it update firmware it self
10) You must let it do 2 updates
11) After everything works ok Install Chech firmware from Gadget Bridge
Hope this guide will help you