Unbeknownst to us (me - the planner), all six nights we will be in Paris in late Sept/early Oct encompass Fashion Week. We're staying in a St Germaine apartment ... wondering if our stay will be impacted at all by the events associated with Fashion Week. If so, what would be the places throughout the city to avoid? Thanks.

September and early October are always very busy in Paris as there are many more events/conventions/ than just Fashion Week. You'll probably not notice much other than hotels are more expensive.

There is no "e" in St Germain.

When we were there in September 2018, we had Paris Fashion Week and the Ryder Cup!#! Whoops!
This year in May, we planned well but then we had the relocated (from St. Petersburg) European Football Championships. It was a fun energy, but the more casual restaurants were packed.
For Fashion Week, it seems like the venues were scattered, we even happened upon an outdoor show catwalking next to the river. I would just suggest to get your dinner reservations soon, especially if you are aiming for something special, but even so, a lot of the support team members will be filling up everything else.

Most people in Paris have nothing to do with "fashion week" and don't care. There really aren't all that many people involved in that event. It isn't public. I seem to recall sometimes they have shows in some area related to the Louvre or the underground Carousel tunnel part, so I suppose if so, that would be closed to the public, but you would find out about that if you tried. I'm not sure where they did that was public anyway.

It shouldn't have any effect on you. I've been there and it had zero effect on me but I don't frequent the kind of places such people would go anyway, people involved in that. They aren't busy going to museums when they are involved in their work project, and they aren't taking the metro or buses.

FYI St Germain is a male, you never will see St Germaine on anything official or French
.

"There is no "e" in St Germain"

Thanks for the info regarding fashion week.

Yes, I do know there is no "e" in St. Germain - typed too fast and too late to edit when I did see it.

Other than Fashion Week, there will be other events in October 2022 like two huge city-wide celebrations of art and culture, White Night (Nuit Blanche) and ParisArtistes.

Fashion Week can be ignored, but it is still a busy period.