microservices – How can we design view count on videos website like youtube which needs to be highly optimized

As per my understanding :

We can have a backend scalable microservice MS1 having an API. Client calls the API in case of a user plays a video. This microservice will be using a sharded cache C1 and a message broker MB1. The cache C1 will manage video count for videos<VideoId,VideoCount>, for every new request it will increment the count in cache C1 and will add the request<VideoId,UserId> to message broker MB1.
On the other side of message broker MB1 a service MS2 will update the request in Database DB1. The sharded cache C1 will fetch data in case of unavailability of data, from the MS2.

Recently, I was in a interview where the interviewer asked me to design this view count which should be scalable. He was only concerned with millions of connections created with cache C1 in case of millions of request.
And I was under impression that the cache C1 is scalable so it’s not an issue.

I have designed similar thing before in some project including like and dislike count. So same way I tried to explain him but he wasn’t convinced .
I tried to find some standard approach or algorithm to optimize it further but unable to find any over google, so finally here I am here. Kindly help me, have I done anything wrong.