I've been playing in my 1.15 world and I'm trying to find netherite. Do ancient debris spawn in a chunk that has been loaded from previous versions or do I have to go to new biomes to find ancient debris?
To download the other ones you need to make a folder in the versions folder for minecraft and put the client and JSON file for the versions in there. They all need to be named the same aside from file extensions. Once you do that, you will be able to choose that version when making a new profile with the minecraft launcher.
sorry to post on this thread a month later, but here's something that can help you figure this kind of stuff out in the future
Imagine getting a "cake kit" that includes strawberries and vanilla frosting. Then a month later you get an updated one with all that + blueberries. You made another cake with the old kit, but it won't have blueberries in it because the kit didn't have them at the time. You have to make a new one in order to get the new blueberries.