Layout differences in Firefox, Chrome, Edge

About the Container settings: I see a totally different setting screen? I don’t have the option you show. And my paddings are already on 20 left/right.

David was NOT talking about the padding value you've set, but the Content container type, I'll re-link the document below:
https://docs.generatepress.com/article/content-container/

Another issue in the mobile view is the name of the author of a quote:

It's because the text's line-height is set to 0 by the plugin
https://www.screencast.com/t/WyWJGRycJG1

Try looking for a setting within that plugin. If you can't find it, I would recommend reaching out to the plugin's support.