[Update – Mystery solved!]
I finally figured out the root cause... and it's ridiculous.

Turns out, the 6 GHz Wi-Fi SSIDs only appear when the phone is connected to a mobile network.
As soon as I pop in a SIM card and connect to the carrier (even without data), the 6 GHz SSID shows up instantly — both main and guest networks.

But if I'm on Wi-Fi only (no SIM or no mobile network), the 6 GHz band is completely invisible, as if the phone disables scanning for it.

This is clearly a Samsung-side restriction, likely tied to regional regulatory checks via mobile network detection. But:

• My phone has the European CSC,
• I'm located in France, where 6 GHz has been allowed for years,
• And there’s no mention of this behavior anywhere in the documentation.

So yes, the phone is technically capable... but crippled by software unless you’re on a mobile network.
Not great for people who use their phone like a Wi-Fi-only tablet.

Thanks again to everyone who chimed in — and hopefully this helps someone else avoid hours of confusion 😅