From my perspective a bug - since a “Save” doesn’t honor the setting in Advanced configuration while “Save As” with ticking “Edit filter settings” (just shown the settings but not changing anything) does honor the setting. But maybe a personal misconception (the setting is about -Dialogs).
But my answer - and that’s what I’ve testet before posting - was about “How to set semicolon as a default separator for CSV files”. There was no mention about, that you start with importing a csv file and that’s why this different use case had not been tested in advance of posting my answer.