I'm Singaporean, my 90-day Schengen stay has expired. Can I transit via Zurich from Croatia to UK? [duplicate]

If you are transiting in Zürich between two non-Schengen flights, you do not need to enter the Schengen area and the 90/180 rule should therefore be irrelevant.

The way I see it, the airline should let you board the plane based on your citizenship and would not usually check the length of stay requirement anyway. In Zurich, you should not see any border guard and even if you do, legally speaking, the 90/180 rule only becomes relevant when entering the Schengen area (at which point the border guards have to refuse entry and follow a specific procedure).