Why does my Mac mail differ from iPhone mail?

I'm using the Mail app on my Macbook Air and the mail app on my iPhone with the same accounts (an iCloud account and a Gmail account). I have issues with both these accounts. On my mac mail client it shows that I have 802 mails (of with 712 are unread) whereas on my iPhone it says 456 total emails. This doesn't make sense at all. i tries synchronising the mail account but it didn't resolve the issue. What might be the reason I am facing this? Any solution to fix it?

I even tried an experiment i.e. to delete an email in my iPhone and then after a minute hit synchronise on my mac's Mail app. Result, the email didn't disappear from my mac mail app and continues to exist in the Inbox. Whereas on my iPhone is disappears.

On MacBook Air, 13-inch 2017 running macOS Mojave v10.14.6 (18G3020) with Mail App v12.4 (3445.104.11)

On iPhone XS, running iOS 13.3.1