No matter how many backups (complete and encrypted) of my iPhone or iPad I have made to my iMac, it only shows one backup for each

No matter how many backups (complete and encrypted) of my iPhone or iPad I have made to my iMac, it only shows one backup for each. I take multiple backups e.g. before I make an update and after I make an update so I can recover to either point--Used to work on iTunes backups-previous iMac. How can I get that functionality back--multiple iPhone (iPad) backups to choose from to recover?