This is generally a bad idea:
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adding items to a poll means they will be added late and won’t get many votes
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this is fundamentally unfair to all voters; what if you realize you need to change your vote due to new poll options?
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you can end up with dozens of voting options which is overwhelming
If you really need an open poll, first start a topic gathering poll option feedback as in “what options should be in our poll?”, let that run for a day or two, then gather all the suggested options (within reason, plus consolidation) into a new poll topic.