Error: 'We can't save your changes right now' When Deactivating a Salesforce User

This error is typically caused by the user being set as the default owner within one or more Salesforce configuration areas. From within Setup, search for each area below using the Quick Find search box and verify or update the default user assignment.

Web-to-Lead: Default Lead Creator

Ensure the Default Lead Creator is not set to this user. Click Edit and change to a different user if needed.

Lead Settings: Default Lead Owner

Ensure the Default Lead Owner is not set to this user. Click Edit and change to a different user if needed.

Support Settings: Default Case Owner and Automated Case User

Ensure that both the Default Case Owner and the Automated Case User are not set to this user. Click Edit and change both to a different user if needed.

Process Automation Settings: Default Workflow User

Ensure the Default Workflow User is not set to this user. Click Edit and change to a different user if needed.

Experience Sites: Default Owner in Preferences

Navigate to All Sites - Workspaces and ensure the Default Owner in the Record Ownership section under the Preferences tab is not set to this user. Select a different user if needed and click Save.
Once you have removed the user from all the above configurations, attempt to mark the user as Inactive again.