I checked with Samsung and got the answer that archiving pictures like is other similar apps is not an option (but taken as a suggestion - obviously no hopes at all, as it just a business slang for "don't bother us" or "f**k off"). Sometimes you have pictures of some important documents and bills that you want to keep as pictures, but don't want to see the listed there in mix with pictures from a picnic, party or some weddings, birthdays and similar - so an option to archive them, but not delete them and have them still available to find via app if needed (which is actually a pretty basic option these days in many other app, namely the Google Photos as the most popular alternative) would be quite useful.
Does anyone have any workaround suggestions that doesn't involve just ditching the Samsung Galaxy Gallery app and use a different one?
P.S. If you think the option would be useful, perhaps you can also submit it as a suggestion - in general I have no hope in any results coming from suggestions, but Samsung Galaxy Android devices are always rich in features (one of the main reasons for their popularity), so perhaps a suggestion (if coming from some number of users) would be so wasted...