It’s possible to copy a directory that contains files:
[mariadb1@node state]$ mkdir test
[mariadb1@node state]$ touch test/file1 test/file2
[mariadb1@node state]$ podman cp test mariadb-app:/
It’s possible to install software (like vim) in a container, see Howto manage or customize NS8 podman containers
You could scp to /home/mariadb1/.local/share/containers/storage/volumes/mysql-data/_data/ so the files will be located in the mariadb-app container under /var/lib/mysql