For Buffy that's only on the R2/R4 DVDs I believe, the R1 DVDs are luckily fully 4:3. See https://en.wikipedia.org/wiki/List_of_Buffy_the_Vampire_Slay...

Unfortunately the streaming HD "remaster" is fully 16:9 and badly adapted, not only regarding cropping, but also colors and editing (just google for "buffy hd").