I had a the bearings on hand and enough stepper motor shaft extending out that I thought I would draw up a quick motor shaft support bracket.
fusion 360 source file: https://a360.co/2r8qcwt
Misumi GT3 Pulley in the photo:
Moons stepper motor in the photo:
PSA: I just put this on and am still seeing the belt want to walk forward and a feel a sort of pulse to the motion when sliding the X carriage. I don't know if it is my whole X end bracket flexing or just the motor shaft or both yet. I plan to find out but it might take some time. If you print this and can provide feedback please do.
Update on what I have found. I have been able to minimize the wobble by shimming the right hand side upward which then pushes against the motor casing to align the shaft. The remainder of the wobble I believe to be an issue with my pulley or motor and not anything this part could directly affect.
Yet another update. after much playing I think the issue is more to do with an out of round pulley than purely shaft flex. I went back to the prusa 2gt idler just to check and the stepping feel when sliding is much reduced but still present. I don't love the uneven nature of this current solution and am contemplating a different approach that would attach to both right hand mount points via longer screws to the motor and be adjustable so as to tune the support placement.
3dxtech nylonx CF
rotate to print with left hand side that has the belt visibility opening against the bed.