I posted on this subject last year and (from the T8 ownership point of view) feel a bit less confused once I read the attached 'In house' Volvo publication, which covers the issue from around page 23.
Clearly, with the process of continual software updating the document may not be 100% reliable but it might help!
As for me, I use pre-conditioning (from the VOC app) without being plugged-in, subject to the recognised fuel and battery minimums. ERS (Remote Start) won't work plugged-in, but does un-plugged. As far as I can tell, ERS is the only way to cool the interior with A/C, when circumstances permit. Preconditioning will use fan-cooling only.
<EDIT: Having re-read the doc., it says that Preconditioning will use A/C, which if true, means the A/C compressor on the T8 is electrically driven, not engine driven. TBH, my only recollection when using precon. in hot weather was the fan (only) running, and the interior wasn't as cool as if A/C had been used, but then I've been wrong before.......
EDIT>
Hope it helps!
Andy