Another reply just to give more nuances, learning any version doesn't matter the most, what you'll need to learn is the concepts used in Godot, become familiar with the editor and comfortable with it, know how to get the most of the documentation and online tutorials. After that, you'll be able to use any version of Godot.
Godot 3.5.1 is still a good choice if you want to make physics based game as the new physics engine they made has still some performance issue in some cases.
Godot 4 provides lot's of changes but it mostly name change, containers'properties, Tweens are no longer nodes, File -> FileAccess with a little difference in usage, and so on. You won't have to start from zero again if you move from 3.5.1 to 4.