Can I merge movies into a single folder within Movies

[TheDreadPirate]

There isn't a "Best" way to organize your media. Just the way you want. So you have to find the solution that Jellyfin supports that is closest to what you want.

IIRC (I don't use collections btw), collections can contain both shows and movies. Jellyfin does have the "mixed" library type, but its a legacy capability that isn't well supported and doesn't work very well.

So I think collections is still the best solution for your need, but would require you to manually create them.