Advanced Query: showing "TODO"s with a deadline AND [(not scheduled) OR (scheduled <= today)]

I’m pretty new in query and have tried to modify several query examples, unfortunately, I still failed to get the result I’m looking for. Can anyone help me to write an advanced query showing this result?
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“showing blocks marked as “TODO” with a deadline AND [(not scheduled) OR (scheduled <= today)]”

p.s. preferred to be an “advanced query”(so that I can learn from how you formulate the syntax) rather than a simple query.

Many Thanks!