- From there you scroll down to see the digital signature algorithm used by each certification authority
still wondering why this has to use SHA1
Root certificate are being used only to verify the issuer of intermediary of the TLS certs, which in this case Cloudflare. It is being shipped by default within a browser or an OS. Many sites e.g. Google, DDG, and Binance are also using SHA-1 with RSA encryption, as its root cert.
I don't know the security importance of it in the process of the whole of how SSL/TLS works. But from my understanding, it's the way it is.
For a further reference of how it being used and why it still used, I suggest see: Why is it fine for certificates above the end-entity certificate to be SHA-1 based?