It should be able to HWID/OEM activate and even KMS (at least IoT Enterprise 2019 LTSC could) but with KMS i don't know if the 10y support stands, we'll see when we get the official ISOs.
In 3 years, the Next LTSC will be Windows 11. I have a serious question. If you replace Win 10 LTSC after 3 years, why not use Windows 11 IoT Enterprise? It was released in October 2021 with support finishing in 36 months right on time for next Windows 11 LTSC.
Personally I have bad experience with Windows 11. (While using Windows 11, I want make it look like Windows 10, then I roll back 10). So not right now...!
IoT LTSC 2019 is not real edition, it's identical to regular LTSC 2019, and share all the licenses/activation IoT LTSC 2021 is separate edition, it only have OEM licences regular LTSC 2021 only have KMS and MAK licenses they will not share activation
"i'm going to keep using windows X for as long as possible and then switch to linux because windows X+1 is garbage" heard this a thousand times
Linux as a concept sounds cool but once you start using it It's AWFUL and unproductive. Things take x10 more time to do and major compatibility problems (and stuff that is ported from Windows is worse and features can be missing). I will never use Linux, I've tried so many times, It's just unusable...
Let me put it this way, Windows 10/11 is like a station wagon. It's great but your milage may wary. Windows Server is like a tank, you need quite the force to break it.