Contacts app very, very slow

Recently the Contacts app on my MacBook Pro has slowed to a crawl. It takes forever to find a contact or add a new contact. There is a lot of spinning wheel and not much else.

Things I have tried already:

• Switch off iCloud sync for contacts - made no difference
• Export all contacts to vCard, delete all contacts from the app, delete 'Library/Application Support/AddressBook' - made no difference
• Set up new user account on mac and open contacts - it works fine for the new user
• Looked at activity monitor while the spinning wheel is occurring - Contacts shows as 'App not responding'

This issue only applies to Contacts, everything else seems to run fine.

Any good solutions out there?

MacBookPro 16" 2019 , Big Sur 11.5.2