Would I always know if a sender put a read receipt on an email?

[another20]

I have avoided opening an email from someone for a while. I had blocked them on other communications but didn’t know how to on my email. I have since opened and deleted it - would it have displayed a read receipt notice to me if it had one set?

Probably not. Marketing emails contain a hidden link that executes when the email is opened. That's how they track what's called the "open rate".

Regular personal emails from a gmail or yahoo account or similar don't do this.

Thanks - it was from a regular personal account - I am assuming then that, as I, as the recipient didn’t have to accept/click to on a read receipt notification - it would not have alerted the sender that I had opened it.

Correct. If you send someone an email from a regular personal email account you have no way of knowing if it's been opened or binned. It's the same for the sender of the email you're concerned about.

Unless you've changed your default setting to always allow read receipts. Which you probably haven't.