Loading and saving can be as simple or as complex as you want. Only you can answer that by trying some different approaches.
Load/Save steps:
It might be you can get away with disabling EVERYTHING in your main scene, additively load the other scene, do the second scene stuff, unload that second scene, and then re-enabling everything from the first scene when you come back to it.
As long as the scripts were not written in a way that breaks when you do this, this can viably hide a lot of stuff (it’s all still in memory) while you go do the other part of the game, then snap right back to it.
It might even be all you need. Experiment!!