Client attestation is a mechanism for servers to get cryptographic proof from a client about what software the client is running. Modified browsers, or software like yt-dlp, would have a harder time providing such proof. How hard a time would depend on the security hardening of the attestation mechanism. It'd almost certainly be broken, just as most attempts at DRM get broken, but it would be one more speedbump.
There are legitimate purposes for attestation; for instance, server attestation can allow a user to run software on a server and know that software matches a specific build and hasn't been subverted, so that the client can trust the server to do computation on the client's behalf.
But one of the leading uses of client attestation is DRM.
There are legitimate purposes for attestation; for instance, server attestation can allow a user to run software on a server and know that software matches a specific build and hasn't been subverted, so that the client can trust the server to do computation on the client's behalf.
But one of the leading uses of client attestation is DRM.