It may be opt-in, but website operators can choose to whitelist Tor even on the free Cloudflare tier.

https://support.cloudflare.com/hc/en-us/articles/203306930-D...

The options for Tor are:

Whitelist (trust)

CAPTCHA (visible challenge which the visitor must interact with to pass)

JavaScript Challenge (visible challenge with less friction, testing the browser)

Block (blacklist -- available only to Cloudflare Enterprise customers)