> > Eli Zaretskii <eliz@gnu.org> writes:
> >
> > > ...  So if you could come up with a change to try on
> > > top of Org 9.6 that would change it back to use overlays for folding,
> > > we could try that and see if the slowdown goes away, and take it from
> > > there.
> >
> > (setq org-fold-core-style 'overlays) ; before Org is loaded
>
>    Thanks.  Mitchell and Stefan, can you try this?

I tested setting org-fold-core-style to 'overlays before loading org and
unfortunately it did not help the slowness in the test org buffer. These
are the two lines I tried in separate tests:

(setq org-fold-core-style 'overlays)
(customize-set-variable 'org-fold-core-style 'overlays)