In fact, 4 10s aren't much harder than 4 8s - for me travel time was dominant as I had to physically go run a lab. So I actually kept my salary while getting permanent three-day weekends. And I justified it by being able to get setup and cleaned up outside of normal work hours which was true and glorious.

This is true but in many companies they won't give you the 4 10s option. The reason is that the company can cut 20% pay but realistically set the same targets (where possible). So the expectations don't realistically drop by 20%, just the time you have to reach them and the pay. Depending on how much you were payed to begin with you may find this a reasonable compromise.

I do 4x9. I like it, but with travel times the days can be quite long. When I have kids I want to go back to 4x8 so I can be home earlier.

I did 4x9 also for a while, also with a long (1h15) commute. Was OK for a year, but I was glad that my next job was 4x8 again, with 1 day WFH. So 3 days in the office, 1 day from home. Perfect!

Same here. IMO only one day already heavily improves life quality. Its not 50% in switzerland, but common enough that most jobs would accept.

I did 36 hours for a good while (taking a friday off every two weeks); that was nice, but it wasn't as necessary anymore during lockdown, because I gained an hour a day for not commuting.

But another reason is that because of the corona, our company didn't do as good as expected and they didn't give anyone any raises, so working a few hours extra is a nice increase in wage as well.

Mind you, otoh I could make a lot more if I were to work elsewhere.