I found some complicated suggestions and many simple ones that didn’t work, but a comment to one of them by Vasil Dinkov provided a simple solution to force a redraw/repaint that works just fine:
sel.style.display='none';
sel.offsetHeight; // no need to store this anywhere, the reference is enough
sel.style.display='';
I’ll let someone else comment if it works for styles other than “block”.
Thanks, Vasil!