Use temp mail for a GitHub test account you'll throw away, like checking a Sign in with GitHub flow. Steps, the 20-minute window and when to use a real email.
Temp mail for Snapchat works on most sign-up screens if you pick email over phone. Here's how to verify it, and when Snapchat asks for a number anyway.
Temp mail for Twitter (X) gets you through the sign-up code. Which address to use, what to do about locks and blocked domains, and which X emails you'll miss.