This glitch consists on skipping the cutscenes on the game (which are...guess what? unskippable). what you need to do is watch the cutscene normally, BUT, paying attention to the little saving icon on the bottom right of the screen. once it disappears, you close the game and open it again. this saves about 2 minutes on proving grounds and more 4 if you take in consideration that we have a 4 minute long cutscene in the game. i don't recommend skipping the Bosses cutscenes and cutscenes that are 15~23 seconds long, it isn't worth it.

Note: during proving grounds, after you skip the Destruction Tutorial cutscene, you'll have the Power-Ups cutscene. Before you even click on destruction for the second time, wait until the saving icon on the bottom right of the screen disappears, then you can proceed to the cutscene and then sucessfully skip it.

You can see it being used here: