WiFi sync doesn't work on Fenix 8 51mm with software 11.90 [DFU-ebba8d]

Which WiFi band are you using?  Fenix 8 only connects to 2.4G WiFi band.

2,4 GHz of course. Other bands (e.g. 5GHz) are even not visible on the device despite I'm also in their range. I added 2.4 GHz WiFi (not 1 but 3 from 7 possible) and next successfuly test all 3 connection but I was not able to sync device via WiFi due to error mentioned above. 

I assumed SSID is not hidden.  Is your fenix 8 WiFi status connected? Is your WiFi version 28.83?

from 15 minutes I'm beta tester (firmware has been updated via bluetooth) and now I have

host 12.16,

gps 2.11

wifi 28,84

but this update didn't solve the wifi sync issue (as I expected) so I still get he same error message

yes, ssid is not hidden 

WiFi test in Garmin Connect app when I run 'test connection' is  "connected to wifi ... " but sync or software update via wifi still doesn't work

You are on Beta version.  If you're connected via WiFi, it should sync.   Can you sync with Garmin Express via PC or Mac?

As I mentioned previously, after updating to the beta version, the device still doesn't sync over Wi-Fi. Additionally, Garmin Express is still unable to detect my Fenix 8 while in the same time Fenix 8 is charging the battery.