Why are they not going to show Spider-man into the spiderverse in IMAX or IMAX 3D at this theatre?

I would call the theatre directly and ask.

They arent going to have that show in IMAX because Mortal Engines is going to be playing in IMAX. It could still play in IMAX in the future however if Mortal Engines doesnt pull a big crowd. Unfortunately, animated movies, especially ones targetting a younger audience, rarely get played in IMAX, so it also may not.

Not enough screens