“When someone visits a website using a browser or other software that checks for certificate revocation via OCSP, the Certificate Authority (CA) operating the OCSP responder immediately becomes aware of which website is being visited from that visitor’s particular IP address.”
Let’s Encrypt doesn’t keep that data, and it admits a CA can be legally compelled to start. Microsoft’s root program is the only one that still requires OCSP. Most OCSP implementations fail open, so a missing response breaks nothing. A revocation check that gives way when it fails was never much protection, but it was a reliable log of where you browsed.