So, I've been messing around in tinkercad and trying to learn Fusion360, but haven't managed to get at what I think is needed for the Ender-3 Y- Belt tensioner. I think what needs to be done is to make your X-Axis tensioner symmetrical, and it will also work on the Y-axis (see this one as backing up that theory - https://www.thingiverse.com/thing:3068872) and mount that upside down since on the Ender-3 Y-axis, the top of the belt is the part that needs to be above the extrusion, and the bottom goes in the middle of the 4020.
Do you feel charitable and up to creating the Y-axis tensioner for the Ender-3? Because I think mirroring it given your skill in creating these is may be pretty straightforward for you to do. I do know that several ender-3 y-tensioners exist but they all look so utilitarian compared to yours.