Um, although the old notes officially ceased to be legal tender in 2021, I used them in retail outlets with zero issue very recently (also had a stash of them). The cashier at the Allschwil Migros accepted my old 20CHF bills without even looking up.This was in April of this year.
If you try to change them into USD, EUR or other foreign currency at one of the booths in the airport, I`m pretty sure they'll get accepted.
https://www.snb.ch/en/iabout/cash