Thanks a lot.
So, I will not try to use docker’s overlay2 storage driver over btrfs filesyste, I will let docker use btrfs driver expecting it to work properly and not having any problem.
Here Docker Storage Drivers | Learn the Different Storage drivers of Docker they say it is the recommended aproach and officially supported for SLE linux, but recommended in Ubuntu.
Debian 10 and 11 support btrfs in the kernel with no modifications and support booting from a btrfs partition (only the UEFI partition should be of other type).
So I assume it is well tested.
Answer from Rafael seems to indicate that there is no special reason for not using it. Problems were with devicemapper and they put the request to use well known filesystems, probably in a time were there was no so much attention to btrfs or other COW systems.
I will give it a try.
I will report back my experience (good or bad) in its use.
For now it works smootly and let me change easily filesystem size, add devices, remove them, etc and gives me a confidence that the underlying data is correct and will keep with no errors.
The only precaution is with docker storage driver if is not tested enough, but it seems it has been widely use in SLE (which implements btrfs as defaults storage filesystem from long time ago).