Hello Bsteph5900,
Let's check to see if you are syncing your contacts with multiple accounts. In the Contacts app on your Mac, choose Contacts > Settings, then click Accounts. You can also compare that list to any accounts you had set up on your prior Windows PC.
You'll also want to make sure that the Show Lists option is enabled under View menu at the top of your screen while in the Contacts app. That can help to make sure those contacts are under a different list.
If those contacts were synced using iCloud previously, you can also restore your contacts via the iCloud website using the steps below:
1. On iCloud.com, click in the toolbar, then click Data Recovery.
2. Click Restore Contacts.
Available versions are listed by the date and time they were archived.
3. To the right of the version you want to restore, click Restore.
There may be more versions than can be displayed. Scroll to see them all.
Note: Wait until iCloud finishes restoring your contacts before you change them. During the restore process, any changes you make aren’t saved.
You can also find those steps in this resource: Restore contacts stored in iCloud on iCloud.com - Apple Support
Hopefully those steps and resources put you on the path to reinstating those contacts on your new Mac.
Take care.