I'd add a note in the README that indicates that PRs will only be merged if they fit the project's direction. Let people know to open an issue to discuss a contribution beforehand if they don't want to "waste time" on PRs that will not be merged.
As for the currently-open PRs that do not fit the project's direction. I'd politely close them with some constructive feedback. It will be easier going forward if your expectations become more clear and documentable.
I don't have all that much experience in this area, though. Would love to hear from others about the nuance and etiquette of this kind of stuff.
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