Really interesting concept, though I found this a lot harder than regular Tetris - and I’m already bad at regular Tetris! I agree with many of the other commenters here in that it’s just not clear what constitutes a “loop”. I had been under the impression at first that it would be essentially an outlined square, which I spent several attempts finding little success at forming. When I finally did build a loop, I hadn’t even consciously registered I was doing so, and didn’t manage to see what it looked like before it disappeared. That happened several more times for the rest of that attempt; I have no idea what any of the loops looked like, because I made them all by complete accident. Some kind of diagram, or anything really, at the start of the game that explains what the game considers a “loop” would help a lot.
Otherwise, this is really well-made! The Tetris theme remix in the background was interesting and certainly more climactic than I’d usually expect from a puzzler. I like the dual use of the theme: you don’t just form loops, the board itself is also a loop! (Though, it felt maybe a bit too small to me. Both in a gameplay sense, but also as in, geometrically I think I’d expect it not to loop as quickly. Maybe. I’m not the best at judging those things, though.)