.I no longer have access to any of the computers authorized to plat music.therefore I cannot de authorize any of them as the new Mac I have now isn't authorized . please advise how I can fix this issue

See the "Deauthorize All" button in the second screenshot below in these instructions from Authorize or deauthorize your computer for iTunes Store purchases - Apple Support

See your authorized computers

To automatically sign in to your Account Information page from your computer, click here. Or follow these steps:

1. On a Mac, open the Music app, Apple TV app, or Apple Books app. On a PC, open iTunes for Windows.
2. Sign in with your Apple ID.
3. In the menu bar on your Mac or PC, choose Account > View My Account.
4. 
5. Sign in with your Apple ID.
6. On the Account Information page, scroll to the Apple ID Summary section. You'll see the number of computers that you've authorized with your Apple ID. You can’t see the names of those computers. If you haven't authorized 2 or more computers, you won't see this section.
7. 

If the number of authorized computers listed is more than what you expect, you might not have deauthorized the computers that you no longer use, gave away, or sold. You need to deauthorize all of your computers and then authorize each one that you still use.

How new your Mac is doesn't affect that. The only reason that I know of for the Deauthorize All button not displaying as described in my original post is the following from those instructions:

If you haven't authorized 2 or more computers, you won't see this section.

If you are using the Music app on your new Mac and following the instructions below exactly and if "Computer Authorizations" in the screenshot below shows more than 1 authorized computer and there is no Deauthorize All button to the right of that, contact Apple Support to see if they can help. There is a Get Support link at the top right of this page.

To automatically sign in to your Account Information page from your computer, click here. Or follow these steps:

1. On a Mac, open the Music app, Apple TV app, or Apple Books app. On a PC, open iTunes for Windows.
2. Sign in with your Apple ID.
3. In the menu bar on your Mac or PC, choose Account > View My Account.
4. Sign in with your Apple ID.
5. On the Account Information page, scroll to the Apple ID Summary section. You'll see the number of computers that you've authorized with your Apple ID. You can’t see the names of those computers. If you haven't authorized 2 or more computers, you won't see this section.
6. 

See Authorization vs. association - Apple Community. You should be able to view your account in the Music app and access the deauthorize all command. If you still cannot access it ask for help from Apple Support.

tt2