In Krita 3.1.0, Save/Export dialogue always pre-select Krita Document file type. I don't remember this was the supposed behavior. We don't need Krita to remember last-used file type after closing it. But in the same session, it's very useful for Krita to remember it so exporting large amount of pictures as one certain file type gets easier.
Hm, I tested with 2.9, and it looks like this has always been the case, so I'm changing the category to wish. I'm also not totally sure it would be the right thing to do -- it might lead to people starting krita, save one image as png, then create a new image, add a bunch of layers, and accidentally save that as png again. Krita 3.2 will show warnings about information loss, but even with that, it might not be enough.
I'm not sure if krita 3.x.x appimage before 3.1.0 final worked like this, though. It was the first time in a long while I felt the annoyance of constantly changing the file type from .kra to "All" when exporting a bunch of photos (I do that all the time because >> Our cameraman always takes photos with unwanted angles >> I must use Krita to rotate and crop them)...maybe I was too tired today. XD Anyway, I kinda agree with your idea you've mentioned in Comment 2. I think if we can make the warning like this: 1) Shows which feature(s) (layers, transparency, color depth) the current file type doesn't support, but do not throw general infos at them, we should be precise of WHICH FEATURE(S) so they may ADAPT & LEARN; 2) Tells user to use .kra if they want to keep those information; Then it's OK to let Krita remember the last-used file type.
Yes -- git master actually does that. It puts all the items that cannot be saved to a particular file format in a list and shows that to the user, and then also offers a checkbox to also save the image as a .kra.
I just checked: if I open a jpeg then select save as, it will preselect jpeg.