Wow, that official support page is incorrect.
If you have the US version of the hub, it operates on zwave frequency 908.4 MHz
If you have the UK version of the hub, it operates on zwave frequency 868.4 MHz
All the zwave devices you use must exactly match the frequency of your hub. This cannot be changed after the time of manufacture.
You Need to check the model number of your hub. It’s probably on the US frequency, but you need to make sure.
All of that said, the Z wave frequency assigned to Saudi Arabia is 868.4, the same as Europe/UK.
Different regions have different frequencies because the local frequency used for mobile phones and emergency services communications like ambulances vary.
In some countries, it is illegal to use devices on the Z wave frequency of another region because they can cause interference with local emergency services.
So you should definitely check to make sure that it is legal for you to be operating without a license on the US frequency before purchasing any more equipment.