Hard drive in external enclosure won't mount
I do a quick test before doing anything drastic. The app Mountain has a free trial. I'd load it and see if that will mount your drive. I had problems in the past with external drives not mounting. Mountain has been able to mount them.

Mountain is not a free app but they do offer a free trial. No subscriptions required.

Mountain is a menubar app. When you click on Mountain it should show you a list of all volumes connected to your mac. From there you can click on the Mount/Dismount button.