Because of a recent change in the openresolv package that comes with amongst others the Raspbian/Pi-OS Bullseye releases.
remember this one?
been busy the entire day to find out bullseye (fresh install) reconfigures unbound
the solution is the same, comment out the unbound entry in /etc/resolvconf.conf, however, if resolvconf managed to run with the entry active, it creates a file /etc/unbound/unbound.conf.d/resolvconf_resolvers.conf. You need to delete that file and restart unbound to resume normal behaviour.
The file created on my system contained only IPv6 info (IP address masked):
# Generated by resolvconf
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