The Huawei E3372 is a USB cellular network modem.
It is called a dongle and should connect to a USB 3.x port.
When you buy an E3372, get a new one or an unlocked used one. The E3372 box should contain the dongle and two ariels.
The E3372 needs an internet SIM. In the UK, a good choice is GiffGaff. Buy a new SIM (never a used one) and then choose your method of payment, contract or Pay As You Go. A contract has the usual contract terms and monthly payment method. A Pay As You Go method requires a monthly top-up which can be paid online by card or by using an ordinary GiffGaff top-up voucher. Check with GiffGaff for payment methods. The basic difference is that a contract will be better value but PAYG protects your privacy if you use vouchers.
You must register the SIM online with an email address.
Put the internet SIM in the dongle.
Fit the two ariels in the sockets on the side.
Connect the dongle to the compuer USB port, perhaps with a USB extension cable.
Then go through the Initial configuration below.
The following steps are based on Linux Mint 19.1, Cinnamon 4.0.10, Ubuntu 18.04.1. If you have an older version, maybe now is a good time to save everything on a big hard drive and update to Mint 19.1 or newer. (You can use that drive with a newer Linux.)
The dongle has drivers in firm ware that configure the dongle every time it starts. You need to ensure that the dongle is not trying to access the internet before the computer boot sequence completes.
Click menu > Preferences > Network: the dongle should be listed as USB Ethernet.
If there are any other network devices, you need to disable them before setting the E3372.
Click menu > Preferences > Network Connections > select the option for the dongle in the Ethernet list
> click on the Settings cog icon.
Click General tab > deselect Automatically connect to this network when it is available.
Click Ethernet tab. You should see a Device entry for the dongle. Cloned MAC address: might be the same entry.
> MTU: automatic
> Wake on LAN: select Default.
> Link negotiation: Ignore.
Click DCB tab > deselect Use Data Center Bridging (DCB) for this connection. (Unless you have a good reason to use DCB.)
Click Proxy tab > Method None (or Automatic)
> deselect For browser only.
Click IPv4 settings tab > Method Automatic (DHCP). All other fields should be blank.
Click IPv6 settings tab > Method Automatic, DHCP only. All other fields should be blank.
Click Save.
End of Initial Configuration. Reboot.
Normal Use of the dongle.
When you start the computer, you must wait until all the boot configuration completes before you turn on the dongle. At the bottom right of your screen in the panel, click on the network icon. In the pop-up menu, click on the button for HUAWEI MOBILE for a green tick.
To check the signal, click menu > Administration > System Monitor > Resources. If Network History shows activity then everything works. If there is no activity, leave the window open and watch it for a few minutes as your signal might be a problem.
The speed of the dongle will depend on how hot it gets, so put it in front of a fan !!

Is there a question in here somewhere?

So this 'guide' is for older version of Linux, with providers for one country. And setup instructions are going to vary depending on provider, aren't they??

Or since first and only post it’s a bot but seemed like an odd bot post.

Thanks for the feedback.
The dongle for me is new and it finally works (Feb 2023) but it took a lot of digging in the questions on various Ubuntu/Linux forums. The answers to those questions vary a lot and there was only question I found that was helpful. So I posted the thread for the people running Linux 19 who might be interested in the E3372. I have no idea how many people that could be.
The setup is for Mint and is not dependent on the service provider. The bit specific to the UK is about GiffGaff and everything else is ubiquitous.
The E3372 is 4G / 5G, small, economical and portable, and seems to be equivalent to the change from disks to memory sticks. An E3372 instead of a bulky router, cables/wifi ariel, etc, if the connection is for one computer.