On the sheet where you set up the action button, please add a "Converted?" checkbox field to mark whether the entry is converted.
When setting up the update values action button, please update the "Converted?" field with "Yes."
Please use combine button to merge the button you created in Step 2. with the original convert record button. Besides, You can hide the original one so users won't accidentally execute it.
With the above steps, when the users press the merged button, the system will convert the entry and update the "Converted?" field to "Yes." Hence, you'll be able to recognize the convert status via the "Converted?" field. You may also apply conditional formatting to highlight if necessary.