Something is odd here @joffreyjaffeux cause we should probably have a clear “call to action” when you click on an invite link. “Join Channel” should be somewhere prominent, we should also handle the “read only - till joined” better for channels you are have not joined (the reactions buttons should be handled more cleanly).
Thanks for raising @Canapin we will try to repro and refine here.
From a UX point of view, my personal expectation was that reacting would be equivalent to writing and would result in joining the channel. If that is not the case, perhaps having the reaction buttons be invisible to a non-member would be appropriate to nip the issue in the bud.