You can tell if a paper plate is microwave safe by looking for a microwave safe label on the plate or the packaging.
Also if a paper plate is microwave safe it will be plain white and free of any types of designs or any coatings that could release chemicals that are harmful when heated.
Most of the plain paper plates are microwave safe, although if left in the microwave too long they could burn or start a fire.
But the majority of paper plates without designs or coatings are safe to use in the microwave.
You can test a paper plate in the microwave by placing a bowl of water on the paper plate and microwave it and check and see if the paper plate stays cool or gets hot.
If the paper plate does get hot then it's not considered microwave safe.
If the paper plate stays cool then it's considered microwave safe.
You can also microwave ceramic plates and plastic plats and bowls as long as they have no decorations on them.
And even ceramic coffee mugs can be microwaved as well.