Just had to enter my emergency passphrase again, because dracut had replaced initramfs-tools on my system without me taking notice. While fixing it (re-installing initramfs-tools) I found the reason for dracut being installed:
# apt-cache show btrfs-progs
Package: btrfs-progs
Version: 5.10.1-2
Installed-Size: 3959
Maintainer: Adam Borowski <kilobyte@angband.pl>
Architecture: amd64
Depends: libblkid1 (>= 2.17.2), libc6 (>= 2.8), libcom-err2 (>= 1.43.9), libext2fs2 (>= 1.42), liblzo2-2 (>= 2.02), libmount1 (>= 2.24.2), libuuid1 (>= 2.16), libzstd1 (>= 1.4.0), zlib1g (>= 1:1.2.0), libgcc-s1 (>> 10-20200211)
Suggests: duperemove
Breaks: btrbk (<= 0.25.0), initramfs-tools (<< 0.137~), libgcc-s1 (<< 10-20200211)
byzantium does only offer initramfs-tools=0.132pureos1 while bullseye offers initramfs-tools=0.140 . So if I install btrfs-progs initramfs-tools gets removed and is replaced by dracut.
Why is initramfs-tools in byzantium not the same version as in bullseye?
P.D. corrected a typo and an error in this message: it is not btrfs-progs that is too old in byzantium, but initramfs-tools
P.P.D added tracker issue T1087