Realtek RTL8720DN and RTL8721DM claim 5GHz wifi as well as 2.4GHz and BLE 5. Finding a decent dev-board for them is not easy. Seeedstudio's Wio Terminal is one of the few.
Why would 40 MHz wide channels be /better/ if the spectrum is congested? Smaller channels would be beneficial. Let’s say 5 MHz, and with OFDMA that is what you get. This is why Wifi6 is crucial for the long term viability of 2.4 GHz WiFi.