How can I load an unmodded backup into a modded game?

In Minecraft 1.16.4, I've played on an unmodded world. I want to play with mods, however I also want to keep my vanilla world. I've already created a backup and extracted it however I'm not sure how or even if I'm able to transfer it to my forge version.

You should be able to just put the world in the saves folder, run forge and load the world but the real problem is that if the mod adds more ores you will have to mine in chunks that haven't been loaded you can get around this a number of ways but by far the easiest is to use a mod that adds a dimension that has ore generation