Fischer played 1. c4 in the World Championship match. I know at least once he played 1. d4. I presume it was in a non tournament game, so not part of his canon of games. Perhaps against some random bloke he bestowed the honor of playing at a social function.
b3 e5 2. Bb2 Nc6 3. c4 (SF & Komodo prefer 3 e3) Nf6 (Although SF 041118 at depth 37 plays the game move, SF 10 at depth 41 plays 3…d5, expecting 4 cxd5 Qxd5) 4. e3 (Komodo plays 4 Nf3) Be7 (Stockfish plays 4…d5) 5. a3 (Komodo plays the game move but Houdini plays 5 Nf3) O-O (This is the choice of the Dragon, but the Fish prefers 5…d5) 6. Qc2 Re8 (SF and Komodo both play 6…d5) 7. d3 (SF and Komodo both play 7 Nc3) 7…Bf8 (SF & Komodo both play 7…d5)
It’s well-known that Fischer practically always played 1 e4, sometimes transposing to the KIA especially in earlier years. I’ve speculated that in 1970 Fischer was already preparing for a World Championship match where he would have to vary his openings - and 1 b3 was a way of proving to himself that he could defeat GM’s with even “less sharp” variations.
Fischer also played a “straight Reti” against Santasiere in 1956, transposed to a QP opening agains Di Camillo in 1957, played the white side of a fianchetto KID in a simul in 1970, and played QG/Slav against Hort in blitz in 1970, along with 40 or so Reti’s/KIA’s over his career.