Use of post-quantum cryptography in HTTPS has been steadily increasing. All major browsers, many CDNs, and most TLS libraries implement and by default enable it.
But there's more to the internet than just HTTPS. So I checked which mail servers support X25519MLKEM768 when using STARTTLS.
Unsurprisingly, fewer than 1K of MX servers for the Top1M domains support PQC. The only major providers who do are Google, Yahoo (shout-out!), and Seznam.