OP mentioned blocking cloud providers but didn’t explicitly mention CDNs, and at least with AWS their IP list allows you to filter out CloudFront. I don’t know of a list of second tier relay operators for iCloud Private Relay but I do know that Fastly[1] and Cloudflare[2] were going to be participating, and presumably other CDNs with their larger number of POPs compared to most VPS providers would be logical choices to run it. So blocking only VPS IP ranges might not necessarily affect iCloud Private Relay.
1: https://www.fastly.com/blog/icloud-private-relay-and-a-priva...
2: https://blog.cloudflare.com/icloud-private-relay/
