Which character should I use in a Windows/Linux directory name to place it at the top of an alphabetically sorted list?

Generally underscore _ works best for this, and should be viable for both OSes.

A folder 1

AA folder 2

AAA folder 3

Who cares about readability and logic. My outlook work archives are a mess.

You could always do:

1_Pics
2_New Folder
3_Music
4_Games

I use ! to sort to top, and Ω to sort to bottom. So far haven't had any compatibility problems.

For the curious: the use case for this is when you want to reduce nesting but also want a sort of "soft hierarchy" within a folder. I could separate my music folder into albums and playlists, but then I'd have a mostly empty folder, so instead I put both in the same directory and use prefix naming to sort them.

@

Because why go for the obvious

I use exclamations in Windows ("!!first" will be sorted above "!second" for example)

and "I’m curious what’s the need for the folder to be sorted first that something like folder pinning or tagging"

Not sure what "tagging" would be in a windows perspective, does it have that? and "pinning" could be using the Quick Access bar I guess which I do for folders I want access to GLOBALLY, but if I have many sub-folders, and in the context of THAT FOLDER I am interested in several more than the rest, but outside that folder I don't care less about them, I'll use exclamations so I can find them easier

(Example, I have a TTRPG folder of art assets for maps from dozens of different sources, each with own naming conventions, and two folders !!Sorted and !Working, as I slowly go though the list to find, name, sort, discard and otherwise clean up the list so I can find what I want. If it was called "Sorted" it would be in the middle of the folder structure and a pain to find when I need it, but I also NEVER NEED that sub-folder unless I am working on cleaning up/sorting that data)

Just saying that in Nemo (or whatever the cinnamon file manager is called) you can pin a file/folder to the top through the right click menu, unless I'm remembering wrong. But I haven't used this feature at all so I don't know how well it works for any use case.

no judgements but I'm curious what's the need for the folder to be sorted first that something like folder pinning or tagging doesn't work for you?

A dot.

Generally speaking: If you want folders to be on top, do it in your application. You should not prefix folders with "random characters" to make them listed in a specific place.

If you really want to, you could use A Foldername because A is the lowest Unicode point character that is a letter (0x41) You could also use @ (0x40). I've seen @Foldername in the wild a few times. I would not use numbers, because numbers are stupid, you also cannot easily change them if you want to have another folder between two already existing ones.

Some applications might ignore non-letter characters (what is interpreted as a letter, depends on your locale) on sorting, though. So the safest would be A.