Let me give a more clear detailed answer.
No there aren't anything similar to steam workshop on itch.io for the following reasons:
1-On itch anyone can view/download a game even if not registered with an account unlike steam where you can only view game page but in order to download/play you need to do that through steam platform witch will require a steam account so anyone will user steam workshop is register and can be tracked if tried anything malicious itch.io on the other hand since anyone can view/download a game that mean anyone can user the map editor in your game and this can be a security flaw.
2-On steam to play the game the steam platform must be open on your device so the steam API can be initialized on itch.io however you can play the game without having the itch app witch if your game has dependency on itch app it will not function properly.
there is something you can do but not sure it will satisfy you can make a separated page on itch and put it under the "Game-mod" category and make any map made by the user pass through you(tell them to send you the map so you can approve it then upload it on that page) hope this is helpful