Imo, transdimensional sounds like something that can go across from one timeline into a completely different space-time continuum without affecting the whole thing(??)
interdimensional is for things that exist within the same space-time/timeline just separated by some weird powerful/strong spatial barrier (or many barriers) and for worlds that don't interact or intersect within (or reside inside) the same Universe/timeline/space-time continuum/spacetime/timespace. basically for pocket dimension, pocket realities etc. (Without affecting the whole thing too???)
That is just my opinion though, and i could be wrong. im not an english major, or rocket scientist lol
"inter- a prefix occurring in loanwords from Latin, where it meant "between," "among," "in the midst of," "mutually," "reciprocally," "together," "during" (intercept; interest); on this model, used in the formation of compound words (intercom; interdepartmental)"
"trans- a prefix occurring in loanwords from Latin (transcend; transfix); on this model, used with the meanings "across," "beyond," "through," "changing thoroughly," "transverse," in combination with elements of any origin: transisthmian; trans-Siberian; transempirical; transvalue. Chemistry."