This specific tangram was incredibly dumbed down (made easier) by using only 4 pieces, and it is still challenging. I can't imagine the horrors if the dev used all 7 Tangram pieces. It would certainly have been much harder.
The game is absurdly laggy for a puzzler. Made me fail speedrunning the levels more than once. Reducing quality barely helps (if it even helps anything in the first place).
The author provided a walkthrough, which was nice, but kind of made it too easy for everyone not up to the challenge. Luckily (or maybe not) the game cannot be paused so walkthrough-checking will still take a toll on player time.
Two tips to those longing for the "Fastest Puzzler" medal:
1- Play only levels 1 to 5.
2- Memorize the first 5 levels solution for this, you won't need any more than that. The walkthrough isn't really needed, but helps.
3- Don't bother reorganizing all pieces position or rotation. Just remember what goes where and do that as fast as you can. Images are accepted in any rotation and even if mirrored.