Nitter's been dead for about a year at this point. I'm pretty sure any Nitter instance still running is using some abstract method and not the actual Nitter system.
"Guest accounts" were accounts you could generate to access Twitter without actually signing up, but then Elon Musk killed them so then Nitter was basically declared dead because most people don't want to spend time making tons of actual accounts to run a Nitter instance and then Elon Musk also made the ratelimits stricter so you needed even more accounts.
Some of the bigger Nitter instances used thousands of guest accounts.