This is just a report of what happened to a 1,5 year old watch with recent updates.
My Fenix 6x pro (non solar) was running SW 16.30 just fine until a point where I noticed heavy battery drain - 1h in gps would eat up 100% of battery. This happened a couple of days before we saw 16.60 officially out.
I made a factory reset (from menu) but it didn't help at all. I made a hard reset (as described here https://forums.garmin.com/outdoor-recreation/outdoor-recreation/f/fenix-5-plus-series/149936/hard-reset-firmware-reinstall-data-location-and-backup?ReplySortBy=CreatedDate&ReplySortOrder=Descending) and it didn't help as well.
Without BT connection it would survive maybe 2 hours in gps mode, with BT as before - no more that 1 hour (note, I did not install any apps, watch faces, data fields). Then, 16.60 rolled out - I installed it via webupdater. After reset Fenix was unresponsive - stuck on default watch face with no time movement. After making and other hard reset, I was stuck with a tactix (!?) watch face and no response whatsoever.
I reached Garmin support and got a SRR number.
Given the number of threads with various problems with 16.60 - I'd stay away from it until garmin says anything.