“Making” is actually the noun here, a singular noun, the subject of the sentence. “movies is an object, not the subject.

just like “running is fun”.

right, you wouldn’t say “running are fun”.

it’s the same thing. you say “making is fun”, whatever it is you’re making.

Like, you wouldnt say(i hope) Is you going to the movie. It’s ARE you going.

Making movies IS fun.

forms of “to be” are hard. I’m struggling in french verb forms so i get the frustration here.

“Making movies ARE fun” if there is a special kind of movies called “making movies” (but I’ve never heard of those :))

So I’d definitely go for IS :))