Hi @sarv123 ,
Thanks for writing into Amplitude Community! Great to see people posting questions here!
Amplitude is an events-based platform so it will query on events and their filters at the time they occurred. So I believe the reason that you are not seeing anything pop up for the chart is that you do not have any Start Session events where the platform=Web at the time of the event. In order to fix that, you would need to make sure you are sending the platform with the Start Session event.
I can see the platform of individual users by clicking on view users and going to their User look-up.
I assume this is at the top of the profile? This would be the most recent value they have which they have gotten from an event. If you go through the Start Session do you see the platform=web attached to it? If not, it would have attached in a different event and this would now be the most recent user value and would be at the top of the page. Does that make sense? If you wish, you can PM me the chart URL or comment it here and I can have a look for you if you are still unsure? Thank you!