Having trouble copying this parallax effect

I’ve watched this video and would love to be able to recreate such an animation on my site’s client. Unfortunately, in this video there are a lot of things that are not showed on screen so I had to be “creative”. Since I’m a beginner, well… it doesn’t work.

The page loader seems to work fine (1’30 in the video) but I’m worried that the text from the page loader aligns with the text in the menu on all devices. Is there a simple way to alway aligne both texts (the one that says on my site “Des pétitions en 7 étapes…”

Where I’m struggling (A LOT) is for the parallax animation (7’30 in the video). I did a breathing animation for the pictures to move constantly. This looks like it’s working properly.

But when I try to use a parallax effect (adding movement to a picture, it looks super laggy on my screen). Also, I don’t know how to setup the trashcan (in the video they use a head) so that it sticks to the screen.

Why do some animations work and some don’t? Am I doing something wrong? (I’m sure I am haha)

Thanks a lot in advance.

Here is my public share link: LINK
(how to access public share link)