I'm still amazed there are people whose job it is to make websites (yeah yeah or apps) that have not read A Dao of Web Design or Responsive Web Design
https://www.webdirections.org/blog/it-was-20-years-ago-today/
https://ethanmarcotte.com/wrote/responsive-design-at-10/
For the record I also recommend Resilient Web Design https://resilientwebdesign.com/
Server run by the main developers of the project It is not focused on any particular niche interest - everyone is welcome as long as you follow our code of conduct!
For the record I also recommend Resilient Web Design https://resilientwebdesign.com/