There is one Youtube channel that is relatively small even though it’s very useful and helpful. I was always struggling to find some materials on more advanced perspective (I know basics, I want to practice advanced skills), and this channel is one of two resources I’ve found that has been useful for me. The videos are in Polish, but they have English subtitles and I haven’t found a similar resource in English.
The link is here: https://www.youtube.com/c/CreosferaStudio/videos.
Do scroll down or visit the playlists: https://www.youtube.com/c/CreosferaStudio/playlists to see especially the basic tutorials, since there are some series of videos from around 2015 that can come in handy, especially if you don’t know perspective much yet.
There are some videos on subjects like drawing trees and foliage with tips and tricks, there are specific big drawings you can follow along (for example this: https://www.youtube.com/watch?v=QFi41p2rVC0 showed me how you can actually a draw a landscape, with explanation how to put trees in equal distances and whatnot - I don’t have that one drawn but recently I drew the treehouse instead: https://www.youtube.com/watch?v=rSYRrEDYI04).
I hope it can be useful to someone.