What FPS will I get in Forza Horizon 4 at 1440p?

At 1440p Ultra native, expect around 180 FPS. With DLSS Quality you can push higher.

Does GeForce RTX 5090 AORUS XTREME WATERFORCE support DLSS or FSR in Forza Horizon 4?

Yes — Forza Horizon 4 supports dlss2.

Yes — the GeForce RTX 5090 AORUS XTREME WATERFORCE runs Forza Horizon 4 at approximately 240 FPS at 1080p Ultra (native, no upscaling).

✓Yes — Excellent

Expected: 240 FPS @ 1080p Ultra (native).