Serviio

I would like to be able to specify the presentation category order.

E g I'd really like to see the order

Series
Movies
Folders
...

but Serviio always sends the menue of categories in alphabetical order.

Actually, that's your player that is doing that, not Serviio. When I look at the presentation list in MediaBrowser (which provides the native order) I see them listed as Titles, Movies, Series, Folders, Last Added, and Playlist. But when I use Kodi on my Shield players, they are listed alphabetical as you mentioned. However, my Roku devices all show it in the same order as MediaBrowser, so it is possible for the player to show them in the order given by Serviio.

All that said, you cannot alter the order in the Serviio console to rearrange the presentation order. I could see a benefit of having such a function, but as I mentioned some players will ignore the order and sort them the way they want, regardless of what Serviio is providing.

Does the same apply to file order?

I use Serviio mostly for audio files, which at the lowest level I have organized by album. When drilling down by folder/artist/etc. having things ordered alphabetically works well for me, but when in a folder (which for me equates to an album) I'd like the files to come up in track order.

Yes, I believe it will be player driven how the tracks are displayed. You could control the order by the way you name the files themselves, for example by putting "01-" at the beginning of the first track you want to play, "02-" next, and so on. Then when viewed in Folder presentation you should see them in the order you want them to play. I can't say if that would also change the order of the files under Album presentation or some other selection.