On Fedi and in the Agora, it seems as if the community is settling on treating #FooBarBaz as equivalent to [[foo bar baz]]. That might be a good fit for logseq, too.
For a single word tag, you can use
For a multi-word tag, you can use
# [[foo bar baz]].
I know that that’s how it works now. Having #FooBarBaz work (like how it works on Fedi) would be a new feature.