Hey, it worked mighty fine, installed C3 litetween plugin from Lunarray from the repo you provided. Just had to remove the box2D from the project object list. Luckily, I did not have used Box2D in important parts of the code. So for now it works.
Need to get rid of the litetween too ASAP, because it won't be supported in june 2021 in C3 :/ Thx for the help :)