When I log in into iTunes, go to Account, View My Account -> I have only 2 devices associated. However when I try to Authorize my laptop Mac Pro 15, I get the "There are 5 devices already associated....". Any suggestions?

Apple recommends using the articles found on their website:

Two articles that could be of use to you are https://support.apple.com/en-us/HT204074 which says “When you sign in with your Apple ID on a device and use that device to make purchases or subscribe to Apple services, the device becomes associated with your account.

You don't need to associate your devices to buy content or download new purchases. You can remove an associated device if:

• You reach your limit of associations and want to add a new one.
• You can't redownload purchases from the App Store or iTunes Store.
• You want to sell or give away an associated device.”

& https://support.apple.com/en-us/HT201251

You can only authorize a computer.

If your MacBook Pro was released in 2013 or later your macOS is due for an update. It’s would still be compatible with the newest macOS Big Sur. I recommend backing up your MacBook then updating the OS.

That is, because with macOS Catalina iTunes is now built into Finder and the music can be found in the Music app.

https://support.apple.com/en-us/HT201475

NPG11 wrote:

When I log in into iTunes, go to Account, View My Account -> I have only 2 devices associated. However when I try to Authorize my laptop Mac Pro 15, I get the "There are 5 devices already associated....". Any suggestions?

See Authorization vs. association - Apple Community. There are two different mechanisms, each with their own list of devices.

tt2

Thank you, but I don't need any assistance unpacking the advice in my user tip. It is our friend NPG11 that needs a helping hand. They have misconstrued an error message that relates to computer authorization as if it related to device association. They need to deauthorize all of their existing devices, then authorize the computers they wish to use. Association has nothing to do with the problem. Upgrading the operating system wouldn't help with the problem at hand and could potentially introduce new ones if they rely on software that isn't compatible with Catalina or Big Sur.

tt2