AFAIK (from my very small understanding of web standards) it's proposed but not yet a standard.

https://annevankesteren.nl/2007/10/http-methods https://datatracker.ietf.org/doc/rfc5323/

And it would work like a get but with post arguments.

Apologies, looks like the w3c proposal is similar but not the same

https://www.w3.org/2012/ldp/wiki/Proposal_for_HTTP_QUERY_Ver...

QUERY rather than SEARCH

How would it be different from `GET` ?

Using post parameters with a GET verb is generally frowned upon and passing search arguments via url parameters is problematic at times (length, special characters, encoding etc).