MTM is a core plugin and shouldn't be uninstallable (only can be disabled)
Nevertheless Matomo shows a working uninstall button
See https://forum.matomo.org/t/fehler-nach-desinstallation-von-tag-manager/30904/8 for more details.
But TagManager is not enabled by default, but also doesn't appear in
So I guess it should either be added to the list (which may have side effects) or maybe a special case for TagManager should be added to