It really gripes me, that everyone is saying THE metaverse.

It's not THE metaverse, when there are multiple competing metaverses - it's just A metaverse then. Facebook/Meta is trying/failing to build A metaverse (and it's even debateable if what they are building qualifies as a metaverse) - and so are those other companies.

You only get THE metaverse, when there is only one. THE internet qualifies for that THE moniker, because it's one big, open, interoperable thing built on shared standards - not owned by any single company, and no matter what browser/device/ISP you are using, you get access to the same whole.