Hope you're not affected by the infamous MBP GPU plague. I have had the internal GPU permanently disabled on mine (GPUmux), which leaves only onboard Intel GPU (garbage)... so my affected MBP also does not load the webpage.

Dual Xeons with RX580 doesn't break a sweat — about 20% GPU load.

I am sorry for that, the web application works better with "Hardware acceleration" turned on, so that it makes use of the GPU. The native apps should perform way better.

Strangely, it runs buttery smooth in my Samsung S21.