The R2 stuff is part of the “Pro” version, but ya… it should work fine on multisite. You would need to put your Cloudflare API token into each site (it could be the same API token as long as the domains are all on the same Cloudflare account (since tokens are per Cloudflare account). And then you would need to enable R2 for each site because you need to pick which bucket to use (which is just a click more or less). You could use the same R2 bucket across multiple domains if you wanted to, but buckets are free, so probably makes more sense to have one bucket per site.
You can see what the “enable” toggle looks like when enabling R2 for a site: https://appforcf.com/styles/default/cloudflare/screenshots/screenshot-17.png
TL;DR: The plugin does work with multisite, each site would need the API token set and R2 enabled (R2 is part of the Pro version).
