New Macs keep asking about old discarded Mac credentials I have only been using modern Macs for a year or so now. I was due to get a 2019 MBP from work in early 2020, so I got a 2009 MBP a few months before that to orient myself.
I created an Apple ID and an iCloud account on the 2009 MBP. With a little difficulty, I was able to apply those credentials to the semi-locked-down 2019 MBP from work.
Since then I have

done a fresh install of the 2009 MBP
left the previous employer, returned the 2019 MBP, and started a new job
bought a 2020 M1 MBA

During the 2009 MBP reinstall and the M1 MBA setup, I was asked for the login password on the 2019 MBP from my former job. I still remembered it, but that kinda freaked me out.
Now I'm about to get a new Intel MBP from the new job. I don't want the credentials from the previous 2019 MBP to be associated with my personal 2020 M1 MBA or the new job's Intel MBP in any way.
Does this make sense to any of you? How can I undo those links and not create any new links from the surrendered 2019 MBP to any future Macs I get?
Update
Thanks to @jaune, I went to my Apple ID web page and looked at the Devices section. The 2019 MBP from my previous employer did not appear. I guess I need to learn more about the keychain, @jksoegaard !
Could it be that you forgot to sign out of iCloud on the 2019 MacBook Pro from your former job?
When setting up a new device, if iCloud Keychain is active, you will be asked to type the login password or passcode of another device that you are signed in to with your Apple ID, see Approve a device to use iCloud Keychain for details.
If you forgot to sign out of iCloud on one of your devices and have given the device away, it could happen that Apple asks you to type the password of that device. In this case, you will have to manually remove the device, as explained in this support article: https://support.apple.com/en-us/HT205064. For example, using the Apple ID website:

Sign in to your Apple ID account page (https://appleid.apple.com), then scroll to Devices.

Click the device to see its details, then click &quot;Remove from account.&quot;


Review the message that appears.

Click again to confirm that you want to remove the device.


For more information on how Apple designs security, see the Apple Platform Security website.