Apple IDs are either third- or first-party. A third-party account is associated with a non-iCloud email address and can be changed when you change your third-party account address. You can create one of either kind and the operating systems all support secondary accounts for various purposes (and in the worst case you can use app-specific passwords, too).
You can convert a third-party ID to a first-party one (I call this process "resignation") by enabling iCloud Mail. You cannot reverse the process (many an Apple fan learns this to their shaggrin, I find).
iCloud gives you three aliases, Hide My Email aliases, and addresses created under your own custom domains; all of these are part of the pre-existing cannon of reserved addresses that cannot be used for new Apple ID registrations.
You can rename your first-party iCloud address to another first-party address, disabling email for the original address in the process. iCloud Mail supports forwarding, so you could still receive the mail that Apple itself sends to the account (and I strongly advise doing that if you do not intend to check its email any longer for that reason). There is, in the worst case, a practical way to distance yourself from a past first-party Apple ID. But you can never dispose of an Apple ID without deleting all data associated with it. This is ultimately why many experienced Applers advise strongly against entry into the first-party purgatory of iCloud Mail on your existing Apple ID, especially if that has a lot of valuable history behind it. In your case, though, you've already taken that course, and the benefit of an iCloud email address, and since it is valuable for your Apple ID to match that address, you should simply rename your primary Apple ID. You can keep your aliases, not lose an address you will never use, and keep all your history.