Ohhhh thank you very much for your detailed answer!!! It is so much more, than I did expect from a forum here. I have an appointment now and will read and hopefully understand your answer til tomorrow.
Only one thing to answer:
Concerning my btrsf layout I have set it up this way:
space filesystem mountpoint Label
8 MB unformatted ---
500 MB FAT32 boot /boot/efi
32 GB LinuxSwap linuxswap swap (1 x RAM)
all GB BTRFS / root
8 MB unformatted ---
Sorry I cannot format it better.
BTW: The thread “btrfs best practice” has been published in the German part of this forum: https://forum.manjaro.org/t/btrfs-best-practice-de/179609