In every field of guitar, there are topics that are or are perceived to be advanced. I don’t think that the guitar education community can agree exactly on what these topics are or exactly what constitutes “advanced”. Advanced is a highly subjective term. But there are some general guidelines that could be helpful.
If our definition of advanced is a professional level, then it becomes easier to discuss. In the world of reading, a guitarist has to go from “I can figure the reading out if I have enough time” to reading the music at sight like you would read a book. There are ways to train that skill and these would be considered advanced.
Developing the ear from being able to figure out simple songs by ear to working out complex songs by ear would be advanced. There are levels of ear training that deal with hearing notes, scales, chords, progressions, harmonies, rhythms etc, etc.
Scales beyond the major and minor Pentatonic and simple traditional scales like major and some common modes would be advanced territory for lead guitar work. Again, we have the problem of the music style involved. What is advanced for Rock and Blues is not advanced for jazz.
Strumming simple chords for a song is more elemental than simultaneously integrating complex chords with melody.
As far as chords are concerned, I would consider open chords, barre chords and power chords to cover beginner and intermediate level guitar. Beyond these chords, we get into “jazz” chords and sophisticated chord voicings that must be considered advanced.
In a field like Bluegrass, simple cut time accompaniment is considered simple. Fast and complex cross picking is considered advanced.
In the long run, “advanced” is wherever you’re not. The goal is to ascertain what you know and where you want to go. With the help of a good teacher, you should be able set up a program that will isolate weaknesses and chart a path to develop the skills you don’t have but will need. Again, I can’t stress how subjective and personal this whole subject is. I have always believed that “advanced” is just the next step from where you are now. It’s a stepping stone to the knowledge and skills you need to be truly considered “advanced”.