On Wed, 30 Dec 2020 08:34:45 -0800, Bob F wrote:

On 12/30/2020 7:13 AM, FromTheRafters wrote:
Rem Ram submitted this idea :
I’m getting a draft through these holes in my window frame. Do these
holes have a purpose? Can I cover them to stop draft?
https://www.homeownershub.com/img/12p9

Just a wild guess, but it might be an access hole for attaching whatever
acts like a counterweight these days. If so, it should have had a cover
for it.

My guess from the pic is that the latch at the top edge of the lower
window pushes a plunger into the hole to securely hold the window open
only that much, so burglars can't push it higher. But I have little
experience with modern windows. There would have been a plastic cap in
the hole originally with a depression for the plunger.
No plunger - that latch is for the "tilt" feature.