Checking in on a Mysql 8.x server the other day I found the following in the /var/log/mysql/error.log
[Warning] [MY-013360] [Server] Plugin mysql_native_password reported: ''mysql_native_password' is deprecated and will be removed in a future release. Please use caching_sha2_password instead'
But not just one of them. Lots and lots of them, one a second, for the last few months. To be sure it didn't seem critical, but having lots of crap in your logs means its obscuring the really important bits, and making it hard to detect real problems.
So how to get rid of them? Well not too hard as it happens. First option is to suppress them in your mysql config. I didn't know this was an option, but yes, you can add the following line to your mysqld config file and they don't get logged any more.