I cannot deploy my website on cloudflare pages, its showing An unknown error occurred. Please try again later

I had the same issue as you.

In my case browser console showed:

Failed to load resource: the server responded with a status of 504 ()

504 is timeout so I disabled uBlock Origin (didn’t help) and turned off my Tailscale VPN connecting me with PiHole.

Not sure if disconnecting the DNS from PiHole was what helped, but after that it started working and I was able to create the website.