For the older AVRs just a quick search online pulled up plenty of pages that went over the instructions explaining what they did and providing examples of how to use them. When I do the same kind of search for the ATMega4809 (for example ATMega 4809 Port Manipulation) I get results for usb port issues, serial port issues, and extremely unhelpful forum posts that end with the person who asked for help being told to read the manual. I've seen the manual, if I understood it I wouldn't be on the forum asking why things aren't working or asking if anyone knew of a resource that did a good job breaking it down 