Cleaning a PCB w/ w/ Isopropyl Alcohol - What Type of Deionized Water Should I Use?
There is no need to wipe/clean the residue of the isopropyl alcohol. Its residue is a white-like stain, mainly around components. Maybe that is why you cannot find any references.
Many times you might as well see in other products this white stain, like here, where someone asks what are those white stains:

And the accepter answer:

It looks like residue from cleaning more than corrosion so gently
cleaning with some isopropyl alcohol should remove it, use a coffe
filter but not a tissue as that can leave fibers in the board. If it
is only a leftover residue it should not impact the performance of the
card.
Is it working as expected? Being an older GPU corrosion is possible if
it was in a humid enviorment for a time but as it is a used card it is
a case of you pay your money and take your chance.
Make sure though it is DRY after cleaning before you power it up !!!
Hope it works out for you
Cheers

He recommends re-cleaning the board with isopropanol, but there is no need, since the white stains will be created once again.
EDIT:
Ok I just read here That the white stain is not a product from isopropanol, but flux residue as you mentioned. I guess you learn things everyday. So yes, try to remove it again with isopropanol.

White residue is generally a symptom of ineffective PCB cleaning.
Common conductive flux residues from the soldering process can include
various unreacted activators, binders, rheology components, and
saponifiers. Among these are numerous iterations of acids (abietic,
adipic, succinic among others), highly basic ingredients (amino
compounds), and even constituents found in “soaps” such as phosphate
and sulfate ions. When a cleaner does not fully dissolve all the
constituents, or the cleaner is not allowed to flow off the PCB, the
remaining solvent can evaporate off and leave behind residue that is
either white or like water spots.