You need to mark them as PDOC (personal document). If you convert to KFX (using KFX Output plugin) this is the default. If you convert to AZW3 you need to use one of several scripts to mark it as PDOC, calibre does not currently have this option.
You could try this one for AZW3
https://www.mobileread.com/forums/sh...d.php?t=364681