My own experience as a Software Engineer in Switzerland:
- A lot of companies are ok with 80% (most often that means 4 days of full time work). Some aren't, but especially towards more experienced roles, it's not out of the ordinary at all.
- 40h is actually somewhat rarer. I've been interviewing recently and lots of smaller companies think it's a point of pride to have 45h or 43h weeks. When you point out to them that this 12.5% rise in hours should also come with a 12.5% pay rise, they are baffled how you would come to that conclusion.
- 4wk vacation is the mandatory minimum. 5wk is nice and often available.
Taking months between jobs and going to 4 days/week is more uncommon though.