Roketto

I ran into exactly the same issue. I follow the instructions and the "Next" button is often greyed out. For example, if I remove the engine in the Intermediate Construction tutorial and then release it, the Next is greyed until I click and hold the engine and only then is the Next button available. Clicking the Science tab does not then ask me to use 2x symmetry and manually doing so does not enable the next button. Perhaps it is an OS issue. I am OSX High Sierra 10.13.6, laptop.