@gargoyle73 said in Vertical Screen Rotation on RP4 400 HELP:
SO what interface do I use to read and alter MAME configs? Can you walk me through steps?
Start the 'File Manager' (mc - Midnight Commander) from the RetroPie system. It has an interface similar to the old Norton Commander, which allows you to browse the filesystem and operate on files/folders. Go to the folder where the retroarch.cfg is located (/opt/retropie/configs/all/) and modify the file by selecting it and pressing F4. This will start an editor, from which you can modify the file and save it afterwords.
There are lots of links with documentation/videos on how to use Midnight Commander - see for instance https://www.tecmint.com/midnight-commander-a-console-based-file-manager-for-linux/ or https://www.linode.com/docs/guides/how-to-install-midnight-commander/.