I do not use Gmail but a self-hosted Postfix instance. I have configured an alias for tagged use only and configured Postfix to reject all emails to this alias without a tag. This means that currently any tag will be delivered but luckily, I am not receiving any spam to this address at all.

Originally, I wanted to create a Postfix filter based on an HMAC together with a browser extension which would simply let me generate new valid email addresses in the form of prefix.HMAC(secret, prefix)@example.com but I have never implemented it.