And neither does a lot of the core jQuery - which is why it has not been updated in the core
phpBB 3.3.x (since Beta1) already has JQuery 3.4.1 implemented.
Nice to know I'm not the only one having this issue . I'm not certain about the CPU usage, I could just hear my PC's ventilator going crazy.
This question has already been answered in this topic.
I just tried it and the input lag is gone .