TL;DR: There is no simple character that works on both MacOS and Windows.
[Wayback/Archive] sorting – Simple to enter Unicode character that would sort after Z in most cases? – Stack Overflow (thanks [Wayback/Archive] sorin and [Wayback/Archive] degenerate):
A
On Windows, none of these options work because they all sort before
A.A solution I ended up using is an Arabic character:
ٴ This folder comes after
zin windows
According to [Wayback/Archive] What Unicode character is this ?, the above mentioned character is U+0674 : ARABIC LETTER HIGH HAMZA.
Note that on Windows the ٴ character displays at the start of the filename, but on MacOS in Finder it ends up behind the extension (as Arabic script is right-to-left) and is very hard to remove. On the MacOS Terminal it ends up on the left and is easy to modify.
The Wiert Corner - irregular stream of stuff 