Back in the days of US CDMA networks, you perhaps had to be more careful to ensure that you selected a device that had the correct Cellular radio capabilities. With the advent of 3G/4G and 5G networks, whilst different countries may use a different selection of radio channel-bands, this is much less an issue.
It is safe to say that if you purchase a device in the country in which it is intended to be used, you will not have an issue - and it will almost certainly operate without any issue elsewhere.
A Cellular Carrier will frequently encourage you to purchase from the Carrier - as they can tie the device to a lucrative contract that makes money. Whether or not this type of contract is in your interests, only you can decide. Be aware that an iPad or iPhone purchased directly from a Cellular Carrier may be Subsidy Locked (limiting your ability to switch to a different Cellular Carrier) or may have the internal eSIM (available on some models) disabled.
You can safely purchase an iPad from Apple. If you intend to later use Cellular capability (or just wish to keep this option available for possible future use), simply ensure that purchase a WiFi+Cellular model. WiFi Only models cannot be converted to Cellular - and, as an aside, WiFi Only models do not include GPS functions (this omission is often missed by purchasers until it is too late). Devices purchased from Apple are not locked to specific Cellular Carriers - and eSIM will be available for use.
Purchase of a Cellular model of iPad does not commit you to using Cellular, but preserves the opportunity to do so.
Activation of Cellular service simply requires a DataSIM to be supplied by the Cellular Carrier of your choice - and, obviously, an airtime contract.
In summary, purchase from Apple if you wish to do so.
