Very neat idea, but execution could use some work.
For starters, explaining some of the controls would be nice. WASD are rather intuitive, and E to interact is fairly common, but it took me a second to figure out the grow/shrink controls for the blue balls, and I never even found out about controlling balls with "F" until i checked settings (I literally just pushed the heart balls around for the first few puzzles lol).
Another point I wanted to mention is that the third-person camera when controlling the ball is way too snappy. If you ever get too close to a wall, the camera reverses and as a consequence, so do your controls. It makes things a bit unfun when navigating tight spaces. This could probably be easily fixed decently well though by moving the camera closer to the ball (the chambers are way too small for the far-away camera) and also by giving the camera a bit of easing in its movements so it doesn't immediately snap.
*POTENTIAL SPOILERS AHEAD*
Something else I noticed is a potential issue with the puzzle featured in the third picture here, the one with the two buttons, a tiny door and a red wall. Is the indended solution here to grab a ball from the previous room, shove it around onto one button using the controllable ball, and then to jump the wall with the ball you control? Because as clever as that solution is, if it is the intended way, it is very jank for a few reasons. first, shoving the ball around with the other ball is a little annoying. Especially with needing to build speed to clear the lip on the button even with the biggest ball size, it was a bit annoying. Second, jumping the wall required me to grow the ball tot he biggest size and reset the size midair. As much as I enjoy platforming tech like this, it would be very annoying and too challenging for a causal player. Thirdly, if you do need the ball from the previous room, you need to make sure the door stays open. I was messing around with the balls, and the big one wasn't completely stationary when i left the room, and the door eventually closed behind me. I had to reset before i was able to use the heart ball in place of one of the blue balls to take it to the next room before getting the heart ball back using the button (which again, feels like it may be unintended, but i genuinely don't know how else you would press both buttons). But overall, the puzzle is totally salvageable, and I liked it, it just needs some work.
And yeah, thats about all the feedback I had. I also think some sound would be nice, but that's not super important. I really enjoyed this little demo, and look forward to seeing what direction you take with this!