If you want to block someone, just tap More on their profile and select Block user. Once blocked, they can no longer send you private messages, and they will be automatically excluded from any meetings you're attending.

To unblock someone later, go to Profile ➞ Blocked Users and tap the X on their picture.

Please use the block feature responsibly, considering that you can also mute members as a first step. Keep in mind that blocking someone also removes their access to shared meetings, so be sure it’s the right step before doing so.