It's just the case that you can't upgrade from a HTTP connect/request to a websocket connection, since at that point the connection is already in HTTP/2 mode and both HTTP/2 and websockets need complete control over the TCP stream.
But: You can still make a HTTP/1 request to the server and upgrade to websockets. Both servers and clients will speak HTTP/1 in parallel to HTTP/2 for a loooong time - most likely forever.
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Websockets won't disappear!
It's just the case that you can't upgrade from a HTTP connect/request to a websocket connection, since at that point the connection is already in HTTP/2 mode and both HTTP/2 and websockets need complete control over the TCP stream.
But: You can still make a HTTP/1 request to the server and upgrade to websockets. Both servers and clients will speak HTTP/1 in parallel to HTTP/2 for a loooong time - most likely forever.