Why does performance decrease on desktop devices when enabling Brotli?

Hello everyone,

Could someone please explain why website performance decreases on desktop devices when enabling Brotli compression?

Here’s the situation. I wanted to test how much Brotli compression improves website loading speed.

For the domain mseaportal.org, I enabled Brotli compression and conducted a page load test on https://pagespeed.web.dev.

Then, I disabled Brotli compression for the site and retested the speed on https://pagespeed.web.dev.

Enabling Brotli compression increased performance on mobile devices and decreased performance for desktops on pagespeed.web.dev. Disabling Brotli compression had the opposite effect.

Can someone explain why this happens?

Thank you in advance.