[f_devd]

This is incorrect, quoting Linux 6.7 release (Jan 2024):

"This release introduces the [Btrfs] RAID stripe tree, a new tree for logical file extent mapping where the physical mapping may not match on multiple devices. This is now used in zoned mode to implement RAID0/RAID1* profiles, but can be used in non-zoned mode as well. The support for RAID56 is in development and will eventually fix the problems with the current implementation."

I've not kept with more recent releases but there has been progress on the issue

[cerved]

Fixing btrfs RAID6 is becoming the Duke Nukem Forever of file systems