@happyyear If the Secondary Document Owners is a multi-person column, the Search for Users (V2) action isn't required. You should be able to pull the email addresses from that column.
Use a Select action instead to get the values from the mulit-person column.

Add a Select action. Insert the dynamic content of your multi-person column into the From field. In my case, it's Assigned To.
Click on this icon to switch from Key value to Map Mode.

Insert the email dynamic content from the multi-person column into the Map field. Important: Once you do this, the select action will automatically nest itself inside an Apply to Each action. This action isn't necessary. Pull the Select action outside of the Apply to Each action and delete it (the Apply to Each action).

Run a test. The Select action will return an array of email addresses. To use these addresses in a Send an Email action you need to convert the array into a string.

Add a Join action. In the From field, insert the output from the Select action above. Email addresses need to be separated by a semi-colon. Insert a semi-colon into the Join with field.

Run a test. The Join action will output a string of email addresses separated by a semi-colon.

In your Send an Email (V2) action insert the output of the Join action into the recipient field. However, I would suggest you use your own email address for testing purposes. You can insert the output of the Join action into the body of the email instead.
This way you can verify who the email will be sent to. Ensure the flow is running as expected before you replace your email address in the recipient field with the actual recipient(s) email address(es)

Hope this helps!
For more flow troubleshooting tips—check out this YT Tutorial: 5 Power Automate Troubleshooting FAQs and Helpful Tips for Creating Better Flows
In this tutorial I cover:
✅ How to troubleshoot a false Condition action result
✅ How to get dynamic content when it isn’t selectable from the list of dynamic content
✅ How to troubleshoot an Apply to Each action that isn’t looping through
✅ How to troubleshoot a skipped Apply to Each action
✅ How to troubleshoot a Filter Query
✅ How to use a SharePoint yes/no column in a Filter Query
✅ How to use Compose actions to troubleshoot a Power Automate flow
✅How to troubleshoot multiple emails being sent
✅ How to troubleshoot multiple Teams messages being sent