Error This user is the default owner of records created by guest users and can’t be deactivated

System administrator or Users who has the permission to deactivate a User is receiving an error, 'This user is the default owner of records created by guest users and can’t be deactivated' when deactivating a User.
 

This error implies that the User is being used as the default owner of records created by guest users in an Experience or Force.com Site.

Select another User as the default owner of records created by a guest user of a community
 

1. Navigate to the Preferences menu of the community

2. Click on Administration tile.
3. Click on Preferences.
4. Under 'Record Ownership' section, change the default owner to another User.
5. Click Save.

You can navigate to the Force.com Site within Setup.
 

1. Go to Setup
2. On the Quick Find Box, type in Sites
3. Select Sites under Sites and Domains
4. Click on the Site Name
5. Click Edit
6. Change the Default Record Owner
7. Click Save.

You should now be able to continue deactivating the User without any error!