But that’s what makes no sense. They cannot be tied to an @mac.com account as there have not been @mac.com accounts for nearly a decade now. They do not exist. There is only iCloud and everything and anything from your @mac.com or MobileMe accounts not migrated to iCloud before 09/2012 quite literally went poof on the internet when those services were shut down that year. It it hadn’t been migrated to iCloud by 09/2012, you simply lost it.
So whatever happened, it happened to your iCloud account, not your @mac.com account since there is no @mac.com account anymore. There are also no @me.com accounts. Both your @mac.com and @me.com addresses are just aliases, nothing more than pointers to your iCloud email inbox.
So you need to remember and clarify what exactly happened when you noticed the missing information for anyone to help. Again, there are no @mac.com nor @me.com accounts. They don’t exist. There is only iCloud..
So whatever happened has to have happened to your iCloud account as that is all you have and all you have had for nearly a decade now.