There’s a spec page that says it’s USB C and USB A and the C ports are only up to 10 Gbps
https://developer.apple.com/programs/universal/
Correct. Those specs are for a non-shipping system. It is a special machine to allow developers to start, well, developing, for the forthcoming 'ARM' Macs.
Those are not the specs for a Mac that is actually for sale. Apple has stated this, several times, that the SOC in the Developer Transition Kit machine is not the SOC that will be in shipping Mac systems. You know, the kind you can actually buy.
Maybe Thunderbolt will be available for 'ARM' Macs. Maybe it won't. But unless you are working on the Macs which will be sold to consumers, you don't know (and even if you are you may not know). I don't know. Most people who work for Apple don't know.
I fully expect Thunderbolt to be available on the first 'ARM' Mac. But that is an opinion. Likewise I expect most everything I run today to run on an 'ARM' Mac (major exception, Windows 10 under Parallels; which is a bummer but - I'll be running my Intel Mini for years, so it won't be an issue for me). And I expect all my peripherals to work. I expect this because Apple said everything that works today will work tomorrow, with specific exceptions.
But like I said, I expect to be running my 2018 Mini for years to come. And it already has Thunderbolt, so I'm not worried about that.