I think I found a bug - at least I can't see how this could potentially be intended behavior. Hope you dont mind my thread title - otherwise feel free to edit.
I just wanted to convert all *.HEIC files to *.jpeg within the same folder, because I thought there's no risk of overwriting due to other file extension.
So I went with these settings.
I did NOT activate "Delete Originals" (left side, previous to last option).

Strange behavior is:
1st it worked (all HEIC converted to JPG, both files kept).
2nd time I tried to increase JPG quality to 92%, and now it got nasty.
I got a lot of errors (dont know why?! Too big JPG files!? (HEIC input files are between 2 and 4MB, so my i7 32gb RAM should be able to handle a conversion to JPG even with 100% quality?)
The output directory looked like this:

Means: All HEIC files which had errors during conversion, got Deleted from the source folder even though no JPG was saved.
Funnily, for the ones where a conversion was successfull, both files, as intended, were kept.
So the bug basically seems to be thta originals without any successfull conversion get deleted!
So you end up with NO version of that picture anymore.
What do you think? Thanks sooooo much!!!!!