https://wccftech.com/doom-eternal-wont-have-snapmap-editor/

At QuakeCon 2018 id Software confirmed that DOOM Eternal won’t feature the SnapMap editor seen in 2016’s DOOM game. However, speaking to PCGamesN Director Marty Stratton didn’t leave the door completely shut off to proper mods.

We had made some technical decisions way back that just pushed us in a different direction than mods. We have spent the last several years making technical decisions that get us back towards being able to do mods.