If it's just playing, you can do it the old way and enable root login over ssh. Then instead of doing
sudo you connect as user
root to your raspberry pi. The relevant lines should be in
PermitRootLogin yes needs to be set. Restart
sshd afterwards (
systemctl restart sshd -- normally runs fine even over SSH :) ). Additionally, you might need to configure a root password:
sudo -s followed by
Note that both: root password and root login over SSH are disabled by default for security reasons. In case you need to operate such a system securely, think twice! Additionally, for any "secure" use case one should generally avoid password login in favour of keyfiles.
root GUI file management is actually very uncommon on Linux. It is not so much a security concern as a large danger of accidentally breaking something (it might be subtle like some trash file being created in a system directory which later causes package uninstallations to fail or it might be direct like accidentally unmounting an important filesystem etc.) Again, if it's just "playing", it might be OK. For real servers it is usually unacceptable.