WordPress is unaware of what kind of database server you’re using, as long as it accepts MySQL flavour SQL, can be communicated with via the mysqli PHP extension, and supports the feature set of the minimum requirements, WordPress is happy.
As a result, none of the concerns you need to worry about are related to WordPress.
Your only concerns should be:
- The dev ops process of installing the new version
- Backing up the database and restoring it if things go wrong
Is it advisable though? I’d say so if it gives you improved security, but that is not a WordPress question, it’s a MariaDB question.
Is there a performance advantage for upgrading centos 7 mariadb 5.5 to centos 8 mariadb 10.3 for wordpress?
There might be, but that’s not a WordPress question, that’s a MariaDB question. I would be very surprised to see a performance loss that is statistically meaningful. You should ask on ServerFault.
Or I should stick to centos 7 mariadb 5.5 to avoid unnecessary trouble?
That’s entirely up to you, and a matter of opinion. There is no canonical factual answer to this. You will need to evaluate how much time it will take to do the changes, and weigh up wether it’s worth the time. Different people will give different answers.