iPhone 14 Pro Max unable to detect 2.4GHz Wi-Fi networks

If the issue is with the phone itself, then you should schedule an appointment with Apple for diagnostics.

Genius Bar Reservation and Apple Support Options - Apple

There is not setting on the iPhone to prevent a 2.4Ghz connection, it is the router that determines if that band is broadcast. Due to the interference and channel overlapping on this band, connecting and/or maintaining a stable connection is much more difficult, so it is not unusual to have a router use 5Ghz only for broadcasting a WiFi signal.

It is up to the router to send out a dual band 2.4 GHz and 5 GHz signal. Some routers allow a user to assign a separate name to the 2.4 GHz and 5 GHz signals. To connect to either the 2.4 GHz or 5 GHz signal, the user must select the specific name of the network and enter the correct password to connect.

Other routers do not have the options to send out separate signals for each bands. In this case, both the 2.4 GHz and 5 GHz signals use the same network name and password. If the iPhone is capable of connecting to either 2.4 GHz or 5 GHz......any iPhone sold in the last 5 years or so can do this......the iPhone will choose the signal with the best combination of signal strength, low noise and speed.

The strongest signal is often not the highest speed signal, since 5 GHz signals are weaker than 2.4 GHz signals and do not penetrate walls and other obstructions as well as 2.4 GHz signals.

If you are saying that your router has been set up to use a separate name for the 2.4 GHz network and your iPhone cannot connect, then you have confirmed that you need to make an appointment at the Apple Store / Genius Bar or at an authorized Apple service shop.

If your router does not have the option to set up separate names for the 2.4 GHz and 5 GHz signals, there is no way to "force" the iPhone to connect to the 2.4 GHz signal. It may....or it may not. It all depends on the quality of the Wi-Fi signal at the location of the iPhone.

In addition to all the really good thing Mac Jim ID suggested, are the networks named as 2.4 GHz or 5 GHz? In order to select a specific network by either 2.4 GHz or 5 GHz the networks should have separate names, like Jim's 2.4 Network or Jim's 5 Network. Named appropriately, you can then choose which one you want to connect to.

Personally, I have an intelligent Mesh Network in my home. My Mesh Network uses both, but I don't have to select which one I want to use. My phone will connect to whichever network it sees depending on my distance from the nodes which are conveniently located throughout my home. Generally speaking 2.4 GHz covers a broader distance and works better through walls, but is not as fast as 5 GHz, which is faster, but means you need to be closer to the router to maintain a connection.