Yes I have this issue to, not sure if it was after the software update. Used to go 8 days between charges, now it runs out within 48 hours and I have not changed any settings. I did a reset, no improvement. Updated manually to software 16.3 and it still uses 50% in one day and that is with one activity. I got rid of apps like spotify and dezer (not that I used them through the phone) and only use a Garmin clock face. I am starting to think that there is a problem with the batteries on the Fenix 6x.
They need to fix this, NOW, because these watches were not cheap.