I printed this a while ago as one of the first things I designed in Tinkercad and printed it when I got my first printer which was a secondhand Ender 3 Pro that came with several upgrades. Add supports manually according to the picture just for the hinges.

The design needs to be slightly modified if you want the leg to fit in the slot perfectly while folded up but if you only need it to prop up your keyboard this will work just fine as I have been using this one printed on inland PLA+ for around 6 months.

Add a cut strip of electrical tape to the flat bottom of the foot to help with sliding if thats an issue for you.