Yes, it is widely known in the epub space that targeting 3.1 or 2 is the more sane option.
With EPUB compatibility issues CSS should always be suspect number 1. Using "modern" CSS features and complaining about missing flex boxz grid, etc is a web developer's mindset.
Just because EPUB shares some of the stack with the web doesn't mean they perfectly overlap (or even should).
Hardly any e-ink embedded e-reader devices use a browser for rendering, they all use purpose built HTML/CSS parsing and rendering toolchains, are baked into firmware and updated once in a blue moon. (If you're interested look at koreader's crengine or Crosspoint reader which runs on an ESP32!)
The blog post reeks of overly confident AI prose. But don't be fooled.
With EPUB compatibility issues CSS should always be suspect number 1. Using "modern" CSS features and complaining about missing flex boxz grid, etc is a web developer's mindset.
Just because EPUB shares some of the stack with the web doesn't mean they perfectly overlap (or even should).
Hardly any e-ink embedded e-reader devices use a browser for rendering, they all use purpose built HTML/CSS parsing and rendering toolchains, are baked into firmware and updated once in a blue moon. (If you're interested look at koreader's crengine or Crosspoint reader which runs on an ESP32!)
The blog post reeks of overly confident AI prose. But don't be fooled.