i would like to know how to check if a iphone 8 plus is unlocked
Try a SIM card from 2 different carriers.
But if it’s been bought from an Apple Store (or Verizon, if you’re in the US), it’s factory unlocked.
Best Buy sell them with a “Flex Policy”, which means it locks to the first carrier it connects to (if it was Verizon, you’re golden).
Hope it answers your question!