Ask questions about dedicated servers here and we and other users will do our best to answer them. Please also refer to the self-help section for tutorials and answers to the most commonly asked questions.
I'm not familiar with Tinyboard specifically, but the error suggests that there is a mismatch between the PHP version and the Tinyboard version. Are you running the latest versions of both, and do the Tinyboard install instructions say that they support the major PHP version that you are using?
You may have to either upgrade Tinyboard or switch to a different PHP version (7.x instead of 8.x, for instance).