Configuring manual protocol selection

We are working on configuring to support HTTPS support for our product. The flow we have is, Browser -> Istio -> NGNIX. We ran into to issues with the “Automatic Protocol Selection” of Istio, i.e., selecting HTTP 2.0 (which is resulting in failure in the upstream at NGNIX).

To resolve this issue, we are attempting to configure HTTP 1.1 (for switching to, “Manual Protocol Selection”).

Istio documentation referred:

Here’s the configuration done:
number: 443
name: http
protocol: HTTPS
mode: SIMPLE
privateKey: /etc/istio/ingressgateway-certs/tls.key
serverCertificate: /etc/istio/ingressgateway-certs/tls.crt

However, this configuration is getting ignored and protocol of HTTP 2.0 is still being selected possibly due to automatic protocol section getting used.
Version of Istio is 1.4.1

Can someone throw light on what could be the reason, and probable solutions?

thanks in advance

Do we need to disable the automatic protocol selection for manual protocol selection?

Appreciate the inputs.