We just experimented with MediaVine Trellis and found that their image optimization did not work well with our custom magazine child theme. Trellis Images did not optimize the photos in the widgets in our category widgets on the home page. We would like to know how GeneratePress optimizes images and whether it would work in a theme like this:
GP doesn’t apply any optimizations ( per se ) to images added to the theme.
If its an archive page then you have options in the Blog module to set a specific size you want to be displayed.
However, we stick to using the core WP image functions for our their output, so there should be no issue with 3rd party optimizers from working correctly. We have many users using similar services without an issue.