If you're referring to this:
There’s no limit on sending single emails to contacts, leads, person
accounts, and users in your org directly from account, contact, lead,
opportunity, case, campaign, or custom object pages.
Then the highlighted part is crucially important. There's no limit to a user going to the page and sending an email manually.
The limits still counts for Apex sending
Intuitively, this makes sense because Apex could sends vast amounts of email and be spamming or using lots of resources.
Users manually sending from pages just can't do the volume to cause issues, so SF don't limit it.
Addition, it seems to be different for Scratch Orgs
Ajay came back and showed more detail. Which implies that he's trying this on a scratch org. I've tried on a scratch org, and had the same result as him: sending an email from the object page, even in Classic used up one of my email limit. But, it does not do this in a conventional sandbox.