Can coming into a lot of money boost your credit?

It does not instantly effect your credit rating.  You could catch up on all your bills and keep them current, and it eventually goes up.  You would likely just pay out your debts.  But millions of dollars in the bank isn't part of your credit rating.  But sure, you'd go to your bank and they'd give you a credit card without problem, or move banks.

Also worth noting that a majority of lottery winners eventually end up broke or bankrupt.

You will be moved to the level of  VIP with the lowest interest rate the bank can offer.