After spending a fair while trying to get a JoyCon strap replacement I liked the closest I found was Po1nt's.

I took his design & modified it a little:

• I'm using radius's instead of a flat bevel
• I moved the latch retainer so that it works more consistently
• I moved the lanyard location to be the same place as the official model

I printed this using 0.08mm layers on a Bambu X1C & it works a treat.

A quick point of note, when putting this onto the joy con have it so the buttons are both facing down, this will prevent the pins interfering with the rail.