Why do you believe this is concerning?
If they’re all from localhost, it just indicates some web application has invalid credentials. If they’re from another host, you probably shouldn’t have made Mariadb accessible to the internet (the default configuration only listens on localhost and there’s a firewall on a default Virtualmin system that does not open the Mariadb port). But, even if they are from another host, as long as they’re unauthenticated, it means nothing bad happened. They couldn’t login so they couldn’t do anything.
You need to be looking at what’s taking time. You could enable slow query logging and see which specific queries are chewing up resources. Odds are extremely high it’s a web application with one or more poorly constructed queries. You may be able to mitigate it by tuning your Mariadb configuration to suit your application(s).
You can also use something like MySQLTuner (GitHub - major/MySQLTuner-perl: MySQLTuner is a script written in Perl that will assist you with your MySQL configuration and make recommendations for increased performance and stability.) to tune your version of Mariadb for your specific hardware.
Also, make sure it’s not some fundamental underlying problem unrelated to the database. Do you have enough memory? If you’re swapping, you don’t have enough memory (having swap usage is not the same as swapping…look at avail Mem and buff/cache in top…if you have a reasonable amount free there, you’re OK, but if it’s low, it’s probably a sign you’re doing too much for the amount of memory you have). Disk speed? Probably not an issue on modern SSDs, but if you’re on a VM that’s on hardware shared by a lot of others, you might be running into limits.