@sajin
Hope you are doing fine, main issue that I see here is that Google uses the same URL/Certs for both personal use and business access (Both are www.gmail.com).
If by chance you access it via a sub domain you could block access to www.gmail.com and allow the sub domain in a previous rule.
Within URL Filtering & Application control you have gmail-enterprise, I cannot test it right now but I'm sure that you need to inspect HTTPS.
Regards,
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