The steps in my previous comment result in the same behavior with all of the following:
Focal systemd version 245.4-4ubuntu3.4 resolvconf version 1.82
Groovy systemd version 246.6-1ubuntu1.1 resolvconf version 1.84ubuntu1
Hirsute systemd version 247.1-4ubuntu1 resolvconf version 1.84ubuntu1
The steps in my previous comment result in the same behavior with all of the following:
Focal
systemd version 245.4-4ubuntu3.4
resolvconf version 1.82
Groovy
systemd version 246.6-1ubuntu1.1
resolvconf version 1.84ubuntu1
Hirsute
systemd version 247.1-4ubuntu1
resolvconf version 1.84ubuntu1