This is a mount for large NEMA17 motors. Tested it on 48mm. No additional idler pulley needed. This mount is also suitable for wide 9 mm belts and 10 mm pulleys.
No supports needed. Please, use the PrusaSlicer screenshot as a reference.
I also added the version with pins for better stability. It should be printed from the opposite side. Cut out the holes for screws and belt after print.
See also
This work contains two parts: this Y-mount and Y Axis Tensioner for 9 mm belt.

It's a remix of Y tensioner for the  Ender 3 Pro with 40x40 V-sot Profile. I want to thank Cornely_Cool as he generously shared step files with me. That helped me to adapt his work for wide 10mm idler pulleys. I used W10T20B5 idler pulley. It fits perfectly for wide 9 mm GT2 belts.
See also
This work contains two parts: this Y-tensioner and Y-mount for huge 48 mm NEMA17 step motor.
Assembly notes
I suggest using a litle bit of lubricant over the screw surface. It will help to insert it into the mount and will also make knob rotation easier.
This is a remix from https://www.thingiverse.com/thing:398515

This is a mount for large NEMA17 motors. Tested it on 48mm. This mount is also suitable for wide 9 mm belts and 10 mm pulleys.
No supports needed. Mount should be printed with pins upwards. After the printing cut the small membrane to insert the profile screws and the belt.
Additionaly, you'll need:
608 bearing x2
M8 screw, 45 mm x1
M8 nut x1
M3 screw, 6 mm x4