Would it be possible to add an option in the next BIOS update for the Optiplex 5050 MT to allow setting any specific SATA port as hot-plug compatible? As it stands there is no such option and, in Windows 10, none of the ports appear as external/removable devices when used.

From what Intel states in https://www.intel.ca/content/www/ca/en/support/articles/000006447/technologies.html, hot-swap capability has to be enabled by the manufacturer or oem.