Oh, I wonder 
#open and close web url by UI button
sleek delta
restive fern
Only i found open but i searched for close
Like i want to communicate with web view
sleek delta
To close the browser, you'll need to rely on external tools or methods outside of Unity's control, as Unity doesn't have a built-in feature to directly close the browser.
ChatGPT
I suppose you can start the browser by using Process, keep the reference of the process, and end it later on another button 
https://learn.microsoft.com/en-us/dotnet/api/system.diagnostics.process.start?view=netcore-2.0
