Don't know if you can help but:

1) Bricked device MODEL, Firmware version, HWID. Garmin Forerunner 920xt

2) Why and how the device got bricked. Nothing weird, just syncronizing with phone, then entered bootloop

3) Symptoms: what's wrong in your device?Constantly booting. Displays garmin logo for 7 seconds then boots again. Hard reset does not work. Garmin logo stays if I press the up arrow button

4) Does your pc sees your device ?Sees it if I connect it while pressing the up arrow button. However garmin applications do not see it.

5) List all the procedures you already tried to unbrick it and their results and errors messages obtained.Soft and hard reset. Connecting to PC but not recognised

6) Do you have Garmin USB Drivers installed ? Garmin: USB Drivers Updates & DownloadsI think so

7) If you don't know HWID get it by Use program G7ToWin to retrieve your HWIDdon't know

8) Write down if you already read or tried GarminCure3 tool - the new way to create cure firmwares for Garmin devices
How to unbrick a nüvi - step by step guideno

9) Can you reach preboot mode? If no ,have you followed this? Garmin devices preboot modeno

10) Probably no , but do you have NV backup?no

Thank you so much