Good question.
When the bonus states "unique" , two or more different eligible offers must be redeemed.
When the bonus states "any of these" , regardless of the number of different eligible offers, the same offer could be used to complete the bonus pending it repopulating/renewing.
If there are no offers displaying, it may or not be active or not available in the area.
In the case of Ibotta bonuses Unique means separate purchases. If the bonus requires 2 unique offers you can't buy 2 on the same receipt and get credit for both on the bonus. You need them on 2 separate receipts to count as unique offers.
Sometimes Bonuses will specify which offers, like I had one for Mt Dew Spark that required the purchase of 2 different offers one for a 20oz bottle and one for a 12 pack of cans. Prior to that I had one for Mt Dew that only required 2 unique purchases of a 20oz bottle and could be regular or diet or zero.