battery discharge faster

And there's new firmware, but does this fix the battery issue, if it fixes it was then incident detection running in background.

Forerunner 955 Software Version 20.29 - 20% Phased Rollout - Forerunner 955 Series - Running/Multisport - Garmin Forums 

I’ve also experienced the bug with floors climbed when driving. Unrelated to battery life of course. For me this wasn’t new to 20.26. I had it on 19.x too

Maybe “Fixed incident detection remaining active after activity” was the case for battery drain and that’s why switching off/on after activity fixed it?

I did not have any activity and it was draining more than usual with fw v20. In the beginning with firmware 12/13 I think when it was new 4-5%, later after v18 I think 7-8%/day now it is near or over 10%. Same watchface, Quatro. I noticed only the day when it was charged the drain was about 8%.

Created support request already on Monday and there has been no response, which would indicate IMHO that this is a known issue and fix is being implemented. 

I have good hopes, though it was external sensor related but did a bike activity yesterday (no sensors) and drain occurred after that as well so a bug with incident detection keeping running might explain this (partially at least).

New update is not available for me yet unfortunately so can't try it out yet...

I think they stopped the update here. Because many are already complaining that the update is not available to them.

I mean, it's phased (20% now) so not surprising I might not have received it yet...

I do get a "Donwload succesful" after a sw update check, but nothing to install... On the computer I see a 006D856710.GCD and secure_config.gcd file in my RemoteSW folder, but both are only 4.71kb so not the actual update.

Patience I guess...

secure_config.gcd ? That was (maybe still is?) an optional file for enabling logs on an Epix/Fenix while in beta. Are you running logs for Garmin Support? (I am but haven't checked folders since it was enabled)