@UnstableApi
    public ClientFactoryBuilder preferHttp1(boolean preferHttp1) {
        option(ClientFactoryOptions.PREFER_HTTP1, preferHttp1);
        return this;
    }
Sets whether to use HTTP/1.1 instead of HTTP/2. If enabled, the client will not attempt to upgrade to
HTTP/2 for {@link SessionProtocol#HTTP} and {@link SessionProtocol#HTTPS}. However, the client will use
HTTP/2 if {@link SessionProtocol#H2} or {@link SessionProtocol#H2C} is used.
This option is disabled by default.
core/src/main/java/com/linecorp/armeria/client/ClientFactoryBuilder.java