This is a support request and not a bug report.
I wonder if 7-zip developers (Igor Pavlov and others) are interested in updating the NTFS attributes letters in 7-zip UI?
Because I maintain this answer in Super User and ntfs_attr.sh shell script (gitlab.com), and I tried very hard in keeping the letters in sync with the (upstream) use in Windows Explorer and attrib.exe in Windows. I would like to share the information so that you can save time figuring out yourselves.
I've seen the "CPP/7zip/UI/Common/PropIDUtils.cpp" in the 7-zip source code, and it seems like the list is slightly out of date, so I propose these:
This is the list of all attribute letters:
"RHSvDAxNTpLCOIEv.x.PU.M......b.."
Uppercase are the letters currently shown in File Explorer, and lowercase ones are either obsolete and unknown. And yes there are same letter assigned to two attributes.
(In ntfs_attr.sh I use a different list "rhsvdaxntplcoieV.X.PU.M......B.." as Unix/Linux systems favor using lowercase letters first.)
Looks like the p7zip project has been abandoned, and I reported the request to the wrong place.
Forwarded to here: https://sourceforge.net/p/sevenzip/bugs/2499/