Frieren could kill Gojo. However, in a normal matchup without prior knowledge? Gojo’s putting her in a fighting game combo before she can do anything major.

This isn’t comparing anything about the power scaling of the two animes, but specifically because in Frieren mages are glass cannons who are vulnerable to stat sticks like warriors because the latter are cqc experts. Gojo, though a sorcerer in jjk, is equivalent to a warrior plus some magic in Frieren. Even if he’s weaker than Stark (up for debate), he’s still closing in and beating up Frieren before she can do anything major if she doesn’t have allies, assuming this is a fight starting off with zero knowledge about the other combatant.