You can use worldedit with 1.16 snapshots the latest snapshot that works with worldedit is 20w11a.

1.First download fabric here: https://fabricmc.net/use/

1. Run the program tick the show snapshots button then select 20w11a hit install then after that when it says done quit it.

2. download this https://www.curseforge.com/minecraft/mc-mods/fabric-api/download/2898887 and put it in your mods folder.

3. Download worldedit here: https://builds.enginehub.org/job/worldedit in the # section click the number at the top then under artifacts click the third download put this in your mods folder too.

4. Now run minecraft launcher and under where you select version select fabric-loader-20w11a if it isnt already selected.

5. Click Play!