Cache for Google Sites

I have a website on Google Sites, but it doesn’t perform well according to Google’s own PageSpeed Insights (see the report). Performance is the lowest score, and the issue is common to any Google Sites’ page, most likely because of the architecture of Google Sites.

Do you know if I could use some kind of cache to speed up page loading?
I was thinking about Cloudflare Signed Exchanges but my impression is they don’t work with Google Sites.