RDX drives are supported by Acronis Cyber Protect Cloud, Acronis Cyber Protect 15 and Acronis Cyber Backup 12.5 as a backup destination. They are treated as a regular local backup location.
If you are backing up to a shared RDX drive with swapped disks, you can set up regular cleanup rules as described in Retention rules
(!) Note that rotating removable drives that you use as backup destinations must have the same drive letter assigned to them.