Hacks to keep track of SaaS subscriptions?

You could use a separate card just for them. There are plenty of banks that let you add virtual cards to your account. E.g. N26 lets you add one virtual card besides your physical cards. So that would allow you to have 1 "SaaS card" and spotting subscriptions is as easy as checking that card's statement.

On the other end of the spectrum are services like Brex which allow up to 10 virtual cards per user, so that you could even use 1 card per service (depending on how many subscriptions you have :) ).

I have auto alerts setup on all my credit cards so whenever a charge comes in I get an email.

But nothing better than that for me.