How to distinguish 5G and 2.4G networks, and find the 2.4G network to connect to.

If your wifi name is "ABC". Seeing that your WiFi only has "ABC" without distinguishing the frequency bands is indeed a common situation for router configuration. There are usually several possibilities:
Dual-band integration (Smart Connect / Dual-band optimization / Dual-band fusion):
This is the most common reason. Modern routers (especially newer models) have the "dual-band integration" function enabled by default or by the user.
Principle: The router will merge the WiFi of the 2.4GHz and 5GHz frequency bands into the same SSID (that is, the "ABC" you see) and broadcast it out.
Device connection: When your mobile phone, computer and other devices search for WiFi, you will only see one "ABC". When the device is connected, the router will automatically assign it to a better signal or more suitable frequency band (2.4GHz or 5GHz) based on factors such as the distance of the device, signal strength, and network requirements.
Purpose: Simplify user operations (users do not need to manually select the frequency band) and try to make the device always work on the "better" frequency band.
Disadvantages:
Sometimes the device may not switch to the optimal frequency band (for example, it is very close to the router but connected to 2.4G).
Some old devices or specific applications (such as some smart home device pairing) may rely more on a stable 2.4G signal, and automatic switching may cause trouble.
Users cannot intuitively know which frequency band they are currently connected to (need to check in the device settings).

The router is a single-band router:
Only supports 2.4GHz: Some very old or very low-end routers may only support the 2.4GHz frequency band. In this case, there is naturally no 5GHz signal, and there will be no "ABC-5G".
Only supports 5GHz: This situation is extremely rare. There are almost no home routers that only support 5GHz and not 2.4GHz. Usually routers support at least 2.4GHz.
The 5GHz band is manually turned off:
Someone may enter the router management interface and manually disable the 5GHz wireless function. In this way, the router only broadcasts the 2.4GHz signal "ABC".
Router does not support 5GHz:
If your router is an older model purchased a few years ago or even earlier, it may not have the ability of 5GHz WiFi natively.

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The above content is for internal learning.

If you are replying and guiding customers, use the following summary.
Assume that the customer's wifi name is ABC.
If the customer only sees the ABC network, it may be that ABC is a dual-band network with 2.4G and 5G. Just click to connect.
If the customer sees two network names, one is ABC-5G and the other is ABC. Then choose to connect to ABC.

If the customer cannot distinguish or the connection still fails, please try to use PLANB.
During PLANB, a wifi list will appear, and the wifi names on the list are the wifi names that meet the connection standards.
Please send planB to the customer for setup.

https://2need9.helplook.com/docs/Set-up-Plan-B