I understand, and I'm sorry I couldn't get it to work. There are a couple of ways I might have been able to detect and fix these kind of version errors, so I'll make sure to implement them in our post-jam version of the game. It's a good learning experience for me, and I'm really grateful you've helped me identify a few more technical issues. Goodnight, and thanks again for persevering!
Oh, and in case you were curious, I can confirm that error is also SDL2 version related. The game uses features from SDL2_mixer 2.6.0 (the current version is 2.6.3), and missing those features will be much harder to work around than the rectangles :(