If you’re giving those companies personal info (name, phone, address, CC) they can track you regardless of what emails you use with each of them.
And if you’re not giving them personal info I don’t see how that works. Yeah so I register on both random site A and random site B with aliases @tfyuhegddssgvd.com, so what? How are they going to find out about each other? What will they tell each other even if they did? And why risk a GDPR violation for such silly reasons?