Cannot downgrade to macOS Sierra on Mac

Yes I tried but again CCC didn't recognize the internal SSD dribe in my MacPro

CCC was installed in an better larger external drive with a perfectly working Sierra system and some apps installed from the appstore

While booting with this external drive the SSD was not visible in Terminal from the External drive. However the computer worked fine with Sierra and every app inclouding CCC in the Sierra Version.

So I think one of the security apps installed when the MACPRO was running on MOJAVE disable this downgrade.

It happened before to me when I had an older MAC PRO and I wasn't anymore able to downgrade to Snow Leopard with a disk purchased directly from Apple.

I also recall Apple blocked some Iphones with something similar but O never had an IPhone so this is only a memory

I said MacPro 2011 as this was the year I bought new from the Apple shop: it it is the version 3.1 and came with SIERRA.

As for the ssd I am abolutely certain I formatted it in another machine with Sierra as MacOS Extended Journaled.

As I said the MacPro 4.1 works with it and so work all other external drives (I only format anything as MacOS Extended Journaled) since is totaly comabpatible witrh the 6 macs I have.

I do not give away anything and I attempt to keep eaqch machine with the latest version of the software they came with.

However the newer they are the worse they seem to be.

But this might be because Apple concentrates on the phone and leaves the computers behind.

Thanks for your reply I am not sure I understood properly: I use Carbon Copy cloner quite often

You suggest me to clone the USB with a SIERRA system to the SSB drive in my MACPRO?

When I boot the MACPRO (NOW TOTALLY EMPTY EXCEPT SOME FILES APPLE INSTALLS IN EVERY SYSTEM UPDATE) The system in the USB pen works slowly but does everything I have in the apps, but both the Finder and Disk utility don't show the SSD internal in the MacPro

How will I be able to clone with CCC if I cannot choose it as the target drive?

Is there something I could do maybe using terminal?

Regards abd thanks

Using disc recovery, the internak SSD was partitioned as GUID and MacOs Extended Journaled. The SSD drive had nothing inside as I erased it all. With the exceptions of the untouchable SSD images, which cannot be touched.

I believe they contained data, or infos or whatever else which not only I am unable to see but cannot erased nor partitioned leaving 2GB or so inside the SSD

I can't remove the SSD disk and use other system to totally erase them as I am not skilled enough to manipulate the MAcPro 4.1, therefore whatever Mojave put inside its SSD disk

All I can say is as follows: as I bought this MacPRO 4.1 it came and booted with MACOS Sierra.

If I now attempt to use Disk recovery and gtry to reinstall the ORIGINAL system the machine came with waiting a rather long time the Apple server offers me HIGHSIERRA to later show me a window telling me the server is not reachable. In Any case I would not install Sierra as the System is already different and is useless to me as a lot of software I used before updating to Mojave was never converted to the newer system and I have several important files I can only read in my small MACBOOKAIR which runs with Sierra, nuit it too smal and slow for any serious work.