It could just be me running a CPU that's too old or an unconventional browser (Microsoft Edge), but the website is extremely laggy (less than 1 update per second) and the tab immediately starts using 80% of my CPU with fans blaring. Got an 8th gen Intel i7 if it matters.
It's a laptop GPU - there's the integrated Intel UHD Graphics 620 card and the dedicated NVIDIA GeForce MX150. Both are pretty old (6-7 years?) but are capable of running most 3D games so I was a bit surprised.
EDIT: P.S. What might help debug is that I have hardware acceleration enabled in the browser, but the GPU is not doing any work on the animejs homepage. For e.g. YouTube, the GPU does a lot of work so I've verified hardware accel works.