Good morning Bruno,
as Guymager doesn't care about file systems:
If you want a HDD image then acquire the whole disk. As you're able to mount the partition directly from the original disk now you also will be able to mount it from the EWF or DD image.
If you just want an image of the partition: Use the "add special device" function of Guymgaer and enter /dev/sdxN, where x is your device letter and N is the partition number.
If you want a logical copy of the files in the APFS partition then Guymager is the wrong tool. Use cp, rsync or similar in that case.
Guy
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Good morning Bruno,
as Guymager doesn't care about file systems:
Guy