Looks like some of the players have struggled in specific levels, so that's hints to every level in game, so you can go further and play other levels:
Level 1, 2 - Swap in different timelines to dodge obstacles (WASD/arrows to move, Space/W/UpArrow to jump, Tab to switch timelines, A/D or arrows to move between them)
Level 3,4 - Use W, UpArrow or Space to climb vines, notice that there are more than two different timelines
Level 5 - Go to left part of level in the past, climb in the future and then return to past, where you can claim the star
Level 6 - Move the box to the right spot, than swap and climb vines
Level 7 - Move the box in the first timeline to the first spot (left), than in the second timeline to the second spot (middle) and etc. than climb vines in the fourth timeline and finally swap and parkour through timelines
Level 8 (the most struggles, as I see, so the most accurate way to complete level) - Move both boxes in the first timeline near the left wall, so you can jump up, but also go the left bottom corner, than swap to second timeline, go to the left bottom corner. Here you need to jump and push the tall box to fall, so than you will can push both boxes to right wall. Than swap again to first timeline, jump to the top, swap to the future, and than fall on boxes and than you will can claim the star
Level 9 - In the second or third timeline push the box to pit, than collect key (press E), in third timeline climb the vines, swap to first timeline, open the door (also press E), and claim the star
Level 10 - Push the box to the left wall in the first timeline, and in the second timeline to pit, collect the key, than open first door by changing timelines and parkouring, than do it again, but now collect key in the first timeline
Level 11 - This level is like previous. Firstly you should use keys in the second timeline, than use keys in the first, also you can have only one key in "inventory" at the moment
Hope, that I help you