01-14-2021, 11:08 PM
Save is for XCF only. Other formats are obtained by File>Export. The rationale is that these other formats won't "save" data that would be useful for further work (layers, selections, paths). So, once you have exported, Gimp may still remind you that the picture is not "saved". You can ignore that, or even complain about it, until you find the hard way that it was indeed useful