Can I use the http method QUERY?

[hrstoyanov]

...even though it is still not approved as a rfc?

https://httpwg.org/http-extensions/draft-ietf-httpbis-safe-method-w-body.html

[Telroshan]

Probably too early as it isn't even mentioned in the MDN doc yet, nor on caniuse
Though, it shouldn't be that complicated to implement since it would just require to define a hx-query attribute.
I would say, feel free to open a PR and work on it, but I wouldn't expect it to be merged until the QUERY method gets approved and becomes a standard