This is with low processor mode enabled. Hell, it's still true when I multiply Low Processor Mode Sleep by 100. This is a blank default project that has a single empty node--and the window is minimized.
func _ready() -> void:
set_physics_process(false)
PhysicsServer2D.set_active(false)
PhysicsServer3D.set_active(false)
Engine.max_fps = 1
RenderingServer.render_loop_enabled = false
get_tree().paused = true