Similar issues on my side. The first two tries got stuck (91% and then 83%).
For the third time, I killed the Fairbuds app on my phone (Android FP5), and then during the update, I kept pressing the screen to prevent it from going to standby. The headphones restarted, but the app kept showing “Updating…”. I killed the app again and then tried to re-do the update, but it just showed me congrats, and I heard the chime in the headphones.
There is a lot of room for improvement in this process.