So what is the abbreviation?

Alright I'm going to give a non-troll response.

All the games only get abbreviated by the first letter unless it has two words or there's a good reason to include the second name. For example, Sun/Moon is SM. SuMo is fucking dumb and literally made up by reddit because in their alternate reality they thought that google searches would bring up Sadism/Masochism and they thought that creating a different tag would help the kiddos, but when a later game was literally one letter off from BDSM nobody said shit.

Following this logic, Ultra Sun/Ultra Moon is USUM not USuUMo.
Sword/Shield is SWSH, but this is only because SS was already taken by Soul Silver in HGSS so the abbreviation is for clarity. I would have preferred S&S but it never caught on.
Brilliant Diamond/Shining Pearl is BDSP as said above.
And Scarlet/Violet is SV. No two letters, nothing like that is necessary, and if for some reason there happens to be a second pair of games in the region it would be best to not have three letters for each version.

Scat

ScVi
We already have an S game

alan!

ScaVi

It's officially SV.
pokemon.co.jp/ex/sv/ja/

Who cares? You guys don't complain when people use RGBY and RSE, both of which use R.

ScVi

SVU [DUN DUN]

Either SV or SCVI

Or GSC and RSE

UUUUUUUHHHHHHHHHHHHHHHHHHHH times change?!?!!? How are you supposed to know which S game you are talking about retard. There are like 15 pokemon games that start with S

SV is enough to tell you it's Scarlet and Violet. If it's not obvious enough from the context, you're the retarded one.

Because these are abbreviations for the pairs or sets of games. You're never gonna see just Pokemon S, it's always gonna be RSE, HGSS, SM, USUM or SV.