Unfortunately, this situation is affecting the system. When I do updates, the Roundcube package goes through its database configuration anew each time. And it will not uninstall using apt; instead it reverts to the database uninstallation dialog, which also immediately fails.
I then thought of trying to uninstall using aptitude, but got this:
sudo aptitude remove roundcube-core
The following packages will be REMOVED:
apache2-bin{u} dbconfig-common{u} libapache2-mod-php{u} libapache2-mod-php7.3{u} libapr1{u}
libaprutil1{u} libaprutil1-dbd-sqlite3{u} libaprutil1-ldap{u} libconfig-inifiles-perl{u}
libjs-bootstrap4{u} libjs-codemirror{u} libjs-jquery-minicolors{u} libjs-jquery-ui{u}
libjs-jstimezonedetect{u} libjs-popper.js{u} mariadb-client{u} mariadb-client-10.3{u}
php-auth-sasl{u} php-common{u} php-intl{u} php-mail-mime{u} php-masterminds-html5{u}
php-mbstring{u} php-mysql{u} php-net-sieve{u} php-net-smtp{u} php-net-socket{u} php-pear{u}
php-xml{u} php7.3-cli{u} php7.3-common{u} php7.3-intl{u} php7.3-json{u} php7.3-mbstring{u}
php7.3-mysql{u} php7.3-opcache{u} php7.3-readline{u} php7.3-xml{u} roundcube-core
0 packages upgraded, 0 newly installed, 39 to remove and 0 not upgraded.
Need to get 0 B of archives. After unpacking 83.3 MB will be freed.
I think that's a recipe for disaster, so I aborted.
Stuck at the moment.