Thank you, glad you enjoyed it! I agree that there should have been some other way then just the exit button after building to switch objects. The idea with the left mouse is that it rotates if you start clicking not on the object and paints if you start out clicking on the object, sorry if it caused confusion (unless you found some new bug). Thanks for the feedback!
(Also the code is a bit of a 𝓂𝑒𝓈𝓈, so idk if it would be useful, but the main functionality comes from here. Basically finding the UV position and stamping a texture there. If I go back and improve the code I'm probably going to post :D)