5N not connecting to reinstalled MacOs via thunderbolt to USB2 cable

Hi! Unfortunately my Drobo support is no longer available. I recently had to reinstall my MacOS. I am running Catalina but my Drobo’s do not appear on my desktop after I connect them via Thunderbolt converted to USB2 cable (I have always used this set up because my iMac does not have thunderbolt). I am able to connect them via thunderbolt on my new Mac Book Pro. Both Macs have the latest Drobo dashboard and I have updated the firmware on the Drobo. Any suggestions?