I tried again reinstalling grub with this commands: Grub2 reinstallation from rescue system
No luck. Therefore I checked with Gparted and KDE partition manager on live system, that I have 3 partitions on my ssd:
- fat32 512MiB with flags boot, esp
- btrfs no flags
- swap
So I guess flags are set correctly which is different than what an author of that post encountered. I also did check and repair fat32 partition in gparted there was no error.
Did short self-test smart in gnome disks it completed successfully.