its not my smoothest run because i became nervous with capturing the video as you can see my erratic movements and one or two near fail moments but you get the idea how to beat this game.

Basically you just move up and down several times in the air. no back or front flips are ever needed.

Important:
for the last level "black sky", for the longest jump segment (from 2:37 to 2:44 in the video), don't panic and just keep holding down mouse cursor, and don't accidentally left click when "click to restart" shows up and that's the only front flip you are ever forced to do.

its much easier than you might think and you can play more relaxed with precise timing and landing, not so much skill or muscle memories are required.

Trivia and tips:
only the first three achievements unlock for checkpoint playthrough.
in order to unlock remaining achievements you need to beat the game without checkpoints. You can disable checkpoint in the settings or it will be automatically disabled after you complete the first run with checkpoints.

If you have a hard time beating certain segments, replay each segment with checkpoints enabled, take time until you get the feel for it before going for flawless run without checkpoints.