Just to note, I tested on Windows and it runs the premade levels fine. (Win10 Pro, 1803, build 1713.590) (i5-6600k, 1080, 16GB)
Maybe a missing dependency? .net framework?
This is awesome stuff from you Walaber, as always! Thank you for letting us try the current state, it's exciting to see where Pro Gymnast is at! This is going to be a definite buy from me, as all of your work is. Too much childhood time was spent happily with stunt, trampoline and gymnast without gratification.
The matt 3D physics are fantastic, it's clear that you have a lot of experience in that area from your other games. The tutorials are very well done, the realtime pose check system you have built is fantastic for training players. This is a great demonstration of learning from usability testing!
My first overall impression is that it handles a lot faster than Gymnast did, maybe something to get used to, too early to say. Currently it's a bit off for me and the slow-motion feature is now a must-use, whereas I liked to do a lot of tries in Gymnast without it. Now it's just too fast to judge when to let go.
The projected trajectory you get in slow-motion is super handy. Is this planed to be a feature to stay or a testing tool?