I don't abbreviate Picard. After the STD Wars of '17-'18, I removed myself from the abbreviation business.
If the series has one subtitle, like Voyager, Enterprise, Discovery, and Picard, it doesn't get abbreviated. Abbreviation only comes into play if there are multiple words, like TOS, TAS, TNG, and the upcoming LD.
DS9, and a hypothetical S31 are special cases, treating the numbers as letters in and of themselves. I also don't abbreviate Short Treks, because ST is too vague and confusing.
If the series has one subtitle, like Voyager, Enterprise, Discovery, and Picard, it doesn't get abbreviated. Abbreviation only comes into play if there are multiple words, like TOS, TAS, TNG, and the upcoming LD.
DS9, and a hypothetical S31 are special cases, treating the numbers as letters in and of themselves. I also don't abbreviate Short Treks, because ST is too vague and confusing.