You must have purchased it as an open box as BB would not sell old stock unless you bought it last year. It is a 2020 27" base model iMac with a 256GB SSD. Nice machine, not a great deal of storage so if your old computer had more than 256GB stored on it you will not be able to use Migration Assistant to migrate to the new computer. That is the first thing to confirm, please tell us how much storage you were using on the old Mac?
Also, when you turned it on the first time did it launch Setup Assistant?