Answer 1

then how the browser render the website ? how about interaction ?

if you meant by hidden is more of a "compile" to secure your rights of the source code, then idk.

as for information leaks, its part of the company resposibility. even though html is visible from client, the delivery can be encrypted. there's a bunch of security measure to protect a web. just check OWASP.

Answer 2

Confidential information is not made visible in the html code. They would keep that stuff as encrypted back end data I would believe.