Your server does not advertise HTTP/3 (the newest, faster web protocol) via the Alt-Svc header, so browsers stay on the older HTTP/2 and never upgrade.
Why this matters
HTTP/3 is roughly a third of global web traffic now. Missing it means slower connections and handshakes, especially on mobile and unreliable networks - a real speed penalty your visitors feel.
How to fix it
Turn on HTTP/3 at your CDN or host (Cloudflare, Fastly and Vercel have a toggle). On self-managed nginx 1.25+, add a QUIC listener and an Alt-Svc header advertising h3.
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