Not playing Abba is a feature not a bug
I just tried “Hey Siri, play Abba” and it worked fine, as did “Hey Siri, play AC/DC”; both started playing in Apple Music. I also tried Hoot’s Mon but it gave me something by the artist Hittman. I’m not sure I can blame Siri for messing up that one. I generally find Siri to be decent for music requests, but perhaps my musical tastes are over-indexed relative to UK chart-toppers from the 50’s. At home we switched from an Amazon Echo to a HomePod Mini, and in that scenario Siri has so far done a better job getting the requested song.
With Google Home, for trying artist names, I usually say something like: Okay Google play the song “foo” by the artist “foo bar” [on device] . It feels very robotic, but usually works. Since I only have one paid music service it usually parrots back what I said adding in “with Deezer”.
Oh I should have mentioned before, I once asked Google Home to play the Star Wars Imperial March and instead of getting what I expected got introduced to something wholly new to me:
You can decide for yourself if this was a happy accident or a misfortune
i asked Siri to Play ABBA…she played ABBA, i asked Siri to play the ALBUM ABBA Gold, she played that album, I asked Siri to play ABBA essentials, and she did (apple music often has a playlist called essentials, ABBA essentials, Neil Diamond essentials, Mozart essentials and so on…) all worked