quickymart:

 

So basically this is all a waste of time. Great 😠

 

Not necessarily.

Assuming you're talking about hosting your own "private" Minecraft server; one easy and safer option is to use a Minecraft server hosting site. There are plenty on the web to choose from. I've not done this so wont recommend any one over the other.  This will come at additional cost (its not significant but may obviously still be a prohibitory to you).

Another option is to use a VM on a cloud provider.

If you are intent on hosting it yourself I believe you still have some options. As far as I know, Spark do not use CGNAT (Im not a customer so cant confirm). 

You will need to do a few things for your child's friend to connect. I'm going to break this right down so if you know much of this apologies in advance:

 

1. Confirm your public IP address. If you google "What is my IP address" you'll get some options to find this out.  It is _this_ address your child's friend will need - not a local IP address (e.g. 192.168.1.X)
2. Optional, but highly recommended: Consider running your MC server on a host who's local IP address is static, or reserved in DHCP. You'll want to make sure this IP address does not change (for step 3)
3. Modify your router to forward certain ports to your Minecraft server's LAN IP address (this is one like the 192.168.1.X). This is different for each router so you'll need to find instructions on how to do this for your make/model. There are reasons you _shouldn't_ do this as you're opening up part of your network to potential attack. But to get things to work you'll need it.  Its been a long time since I ran a MC server (also for my child) and I cannot remember the default ports involved.
4. Ensure that the minecraft server port(s) are allowed inbound access on your PC's firewall. As others have suggested you can disable this - at least for testing (I wouldnt leave it disabled though!).

For testing connectivity I would hotspot to my phone and attempt to connect. This way you can debug things locally.

All in all, I'll come back to suggesting you use a MC server hosting site.