Suntour Raidon 27.5+ 120mm air fork
The Raidon is an air spring, oil damped fork. It sounds like an internal valve is blocked or stuck shut, and that is resisting fork compression and rebound.

Suntour does provide a range of servicing manuals and videos, but unless you are an experienced bike mechanic you should take the bike to a good local bike repair shop and have them deal with it. Suspension forks have very specific servicing procedures that must be adhered to.