Do you have a proxy in front of your site that is changing the protocol version? I have been using that on a dozen sites for years without issue. What browser are you using? Do your access logs show a HTTP/2.0 request? If you have something like Caddy or HAProxy in front of NGinx that is changing the proto version then you can create a similar rule at that outer layer. Or perhaps NGinx in front of NGinx doing a proxy pass?