For now, I succeed to resolve the problem by switching from Transitional mode to Reader mode.
But it seems it will not do the trick for long as Reader mode is legacy.
Thank you for contacting us, AMP plugin allows only 75kb of CSS per page as per the AMP framework rules, The AMP plugin does a CSS tree shaking to remove excessive CSS but in some situations where third party plugin or theme adds additional CSS.
You can learn more about CSS tree shaking using our docs.
From your data, we know that your theme is exceeding the CSS limit.
We will recommend using Reader Mode with an AMP-compatible theme such as Astra or Neve, the Reader Mode theme will be used only to serve AMP pages while non-AMP pages will continue to work with your primary active theme.
You can check our documentation for Reader Mode or watch video below
