My suggestion would be to look at the cf logs (coldfusion-out.log, coldfusion-error.log, etc) to see if there are errors/warnings during cf startup. My first guess is that there's a problem "activating" the CF license.
CF2021 introduced a new license activation mechanism that checks if the license is legit and not used elsewhere, and it does this via a check against Adobe servers. As such, your servers need internet access. There is provision for both specifying a proxy to use (if your network requires that) or for offline/manual activation. There is also a grace period for you to resolve such matters, after which it does revert to the developer edition.
All this is discussed in the docs on activation, here:
https://helpx.adobe.com/coldfusion/using/coldfusion-licensing-activation.html
Or you can of course ask follow up questions here, and Adobe may reply, along with myself or others. And there may well be some other explanation, depending on what you find.
Please do let us know how things turn out.