Mario Godot 4.0 release is imminent according to Reddit, twitter and everywhere really, GitHub 4.0 milestone is also 100% done. So probably next week at the latest.
And yeah, choosing 4.0 over 3.5 is probably not wise, but at the same time all hands on deck are on pushing 4.x forward and for someone new to Godot, learning 3.5 further seems redundant if in 6-8 months 4.1 will be out.
But I can still probably prototype and learn without the animation player.