I want to migrate from mysql 5 to either mariaDB 10.5 or mysql 8.0.21 currently i am using llblgen pro 4 and LLBLGen Pro Runtime Framework for my projects.

Which llblgen pro version should i use? which one (mariaDB 10.5 or mysql 8.0.21) are fully supported by llblgen pro with less changes to my code? (i am still using vstudio 2013)

We test on MySQL 8, not mariaDB. In general mariadb is compatible with mysql 8 tho, but if you're in doubt, mysql 8 is what we test on.