Mac Studio doesn’t offer 4K@120Hz when connected through Yamaha RX-V6A receiver

When I connect my Mac Studio (macOS Sequoia 15.4(24E248)) to my LG OLED55B1RLA TV directly via HDMI, I get full 4K@120Hz support — everything works as expected.

But when I connect the Mac Studio to the same TV via Yamaha RX-V6A AV receiver, 4K@120Hz is no longer available in display settings. The highest refresh rate available is 60Hz.

Things I’ve checked:

• I’m using the same certified HDMI 2.1 cable in both cases.

• The RX-V6A supports 4K@120Hz passthrough (confirmed by Yamaha and multiple user reports).

• eARC is enabled on the receiver and the TV (I also tried disabling it — no effect).

• The HDMI port used on the TV is HDMI 3, which supports 4K@120Hz and eARC.

• The TV displays 4K@120Hz fine when connected directly.

• I’ve inspected EDID data via ioreg, and it looks like macOS is being conservative when audio passthrough is involved.

It seems like macOS is limiting display modes when audio (eARC/ARC) is detected over HDMI, possibly due to bandwidth concerns, even if the hardware supports it.

This limitation does not happen on Windows or other devices connected through the receiver — they can output 4K@120Hz just fine.

How can I force macOS to allow 4K@120Hz in this setup?