The new docs are extremely annoying; if you're still running a legacy app, sometimes you get put into a doc for a feature you think exists, but then you realize it's not for the right version you're running.

Also the new app routers are very confusing. There are concepts of a layout, template, page, etc. While it's nice to have server rendering at this level, it's difficult to understand what is bubbling which direction, and when to use a layout vs a template. Sometimes after building something one way (eg using layout), you realize you actually need to build it using the other in order for specific features to work.

Old Next was great and simple- new Next has become increasingly frustrating and not so easy to adopt.