problem solid division

[eurok8]

I have a problem: having made a body consisting of multiple extrusions, cuttings,etc I joined all the pieces with the combined command.
Then I had to mirror it.
Now I should move the mirrored body sideways, but when I select the mirrored body, I also select the original one, that is, it turns out to be a united body.
I tried to split the two bodies with the split command, but I couldn't.
solutions?

 

[Peppe]

when mirroring your solid select the "new solid" option

 

[eurok8]

when mirroring your solid select the "new solid" option
View attachment 34225

That's it.
Thanks, I forgot to press it, and yet I used it a couple of times.. .