What is the difference between an uncut and theatrical version of a film?

Uncut isn't necessarily the Director's cut unless they so. The uncut version tends to have deleted scenes incorporated into the film, maybe ones that were too gory for thetrical release, or other scenes that were cut for time constraints. Uncut would be better tbh.

Uncut version is the actual Version the Director intended to release as his final version. But due to several circumstances, like Censor rating and critic suggestion during the preview, the movie maybe cut to suit the needs and that is called the theatrical version.

I would say the Uncut version is always better, for example Apocalypse Now Redux.

What film is it? Depending on the type of film, it may just be a difference of one shot of gore or nudity, considering that you said they're the same length. With some newer horror films, I think they just market two versions so they can get two purchases out of some fans, when the difference is very negligible for the most part.

I think uncut versions have all the deleted scenes in the film instead of having them included in the bonus features.