How does dom size affect website speed and theme optimization?

hi!

recently, i have been using an app for image optimization to improve my site’s speed. The app has reduced image size by 400 MB while simultaneously implementing lazy loading, pre asset loading, etc.

BUT apart from this, my site’s speed is the same.

Here is my site: planetjunior.pk

Can anyone check how the dom size is affecting my speed or is there any other reason and what should I do to tackle this issue?