can I merge my itunes account with my apple ID?

Previously asked question. The answer was “no, try using family sharing”. This doesn’t work. I also had a legacy itunes account before we owned any apple computers and way before iPhone. When we set up our first mac years later, they suggested a .me username and we used the original itunes gmail account for our itunes password, since we already had several thousand dollars of music and video associated with that account.

It appears that set-up is no longer supported by apple - ie a different appleid and itunes account for purchases. Family share was supposed to be the answer. But it will only let you share the content associated with the appleid, not the itunes account that has a different id. So all of our music and video is stuck on an account that we can no longer share, or even access unless we’re on a version of os that allows separate accounts. IOS doesn’t appear to support this anymore, it’s just a single id - the appleid associated with that device.

any advice?