Make sure none of the realmd packages dependencies are explicitly listed for removal with a check mark on the "Packages" page. Use the apt depends <package name> command. For example:
apt depends realmd
realmd
Depends: libc6 (>= 2.34)
Depends: libglib2.0-0 (>= 2.39.1)
Depends: libkrb5-3 (>= 1.10+dfsg~alpha1)
Depends: libldap-2.5-0 (>= 2.5.4)
Depends: libpolkit-gobject-1-0 (>= 0.99)
Depends: libsystemd0
Recommends: policykit-1
policykit-1:i386
Then search for these packages on the "Packages" page. Tip: you can click in the "Packages" page and start typing to search through the list quickly.
Also, make sure another package, flagged for removal on the "Packages" page, does not depend realmd.
You can identify which packages depend on another package using the rdepends <package name> command. For example
apt rdepends realmd
realmd
Reverse Depends:
Suggests: gnome-control-center
Suggests: gnome-control-center
Suggests: budgie-control-center
Suggests: gnome-control-center
Recommends: ubuntu-mate-desktop
Recommends: ubuntu-mate-core
Suggests: budgie-control-center
In the above example, all of the listed packages suggest or recommend realmd. So (in this example) realmd will not be removed if one of these are removed. However, if you see the tag Depends:, then realmd will also be removed if the package is removed.
Lastly, you may have to also check that realmd's dependencies are not removed when some other package is removed, because this will cause realmd to be removed as well. This is a little time intensive, but you would use the apt rdepends command on the other packages that realmd itself depends on (libc6, libglib2.0-0, libkrb5-3, etc.).
