The Modern Chess product, Play the Pseudo-Catalan by GM Mihail Marin, also recommends 1.d4 2Nf3 and 3.g3, similar to Keep It Simple 1.d4. In the preview presented here

https://www.modern-chess.com/course/play-the-pseudo-catalan/95221/

Marin specifically comments on the OP's proposed 1.d4 + 2.g3: After 1.d4 Nf6, Marin says, "Tartakower's 2. g3 is meant to be super restrictive by preventing Black from neutralizing the Catalan bishop by playing the Queen's Indian. This move order has a significant drawback, though. Black could play 2… c5!" He goes on to answer 3.d5 with 3...b5, which he calls " the most disturbing continuation" (presumably for White). Marin follows the game Kakulidis,E (2083) -Bergsson,S (2090) Helsingor Kronborg Master-2 2022, giving 4. a4 b4 5. c4 g6 6. b3 Bg7 7. Bb2 O-O 8. Bg2 a5 9. Nh3 Ra7 10. O-O. Now he deviates with 10...e6⇄, which Stockfish evaluates as equal. Marin also gives a few bits of analyses on divergences from the above line. It's a free preview, so it would seem to be worth a look.

So 1.d4 and 2.g3 is the low-prep repertoire I've finally decided on.  Is there any material on it?  Like maybe some solid analysis of Firoujza's win against Carlsen?  Though I do know those reversed Gruenfeld/Exchange lines pretty well, being as I used to tinker with the Gruenfeld before finally switching to the QGA.

In any event, I'm looking for material as to the *plans* against *various* Black responses.  Thanks in advance!