It's really just a warning. If the button is available you can do the regeneration anyway.
For it to work what you want you should previously clone the data disk. So the uuid of both data disks should be the same. After that run regeneration (despite the warning) and everything will work normally. You will have two cloned systems.
Thank you ... but I have more questions for you.
1. How to "previously" clone the data disk?
2. In the regen screen there are two "strange" messages:
NOT ALL DATA UNITS OF ORIGINAL SYSTEM ARE CONNECTED... but the only NVMe is connected. Others NVMe previously connected were unmounted.
IT COULD NOT BE READ the information from System disk (original or actual) . Why?
3. What's the meaning of the last message about the system is already configured ... and I must do a clean installation? I install OMV directly from an image that write in the eMMC deleting all data, etc 