Reconfirming my understanding of the Metaverse

It seems the more I read about metaverses, the definition of it turns really vague to me.

My understanding of it is, it is a platform on the blockchain where people can gather and use coins or NFTs from that blockchain. From your wallet, you can freely exchange these coins or NFTs outside of the platform as well.

For example: Sandbox or Decentraland

But then you have platforms such as Fortnite or Meta for example, that call themselves metaverses but don’t run on any blockchains or use any coins/NFTs. Is that still considered a metaverse?