I would get to the point where you can create simple games in Godot 4.0 first before looking at the GDQuest 3.0 courses. At beginner level, the 3 vs. 4 differences will be too confusing. But once you're at the stage where you're looking for intermediate courses, you can try and tackle the GDQuest 3.0 courses in 4.0 if you're brave. Some API changes are superficial enough, others less so - the forum comments have been very helpful to me. The GDQuest team are working on 4.0 material right now, although I think these will be new courses rather than makeovers for the existing ones.
EDIT: I sound like I'm taking sales commission here, but one more recommendation: the Bradfield book is available as a Kindle ebook, but Kindle's code formatting can be pretty tortuous, and incredibly you can't even copy-paste from the Kindle app without some hack or other. But Packt offer the full book as nicely formatted HTML.
EDIT: I sound like I'm taking sales commission here, but one more recommendation: the Bradfield book is available as a Kindle ebook, but Kindle's code formatting can be pretty tortuous, and incredibly you can't even copy-paste from the Kindle app without some hack or other. But Packt offer the full book as nicely formatted HTML.