[SOLVED] How to shrink BTRFS image

[Nachteule]

You can do it while fs is mounted

First step: shrink FS
btrfs filesystem resize 12G /

Second step: remove swap partition
swapoff -a and then remove this partition

Third step: resize partition
The trick is removing the existing one and create a new one with exactly the same start block and reduced size (16GB minus swap size minus boot part, take 15G

Fourth step: create image
make an 16GB image from this sd-card and write it back to your 16GB card

Last step: fine tuning
If system boots from your 16G card, you can do finetuning
add swap partition
and resize btrfs to max size

All these steps I already did about one year ago