There are two stages to actioning search terms;
Adding search term Actions to a queue, then
Submitting that queue of Actions in a single submission.
This has been done to speed up the process for reviewing and actioning the search terms as the delay created by sending data back and forth via the API for each Action would render the tool too slow to use effectively.
Important to note: You can add search terms to the queue across all the tabs for a given Ad Account, but you will need to submit these Actions for each Ad Account before navigating to another Ad Account. If you do not submit your queued Actions for each Ad Account as you go ...
So the full process to action a search term is:
Apply an Action (such as ‘Add As Negative’ or 'Snooze 7 days') to a search term to add it to a queue.
The kebab menu at the end of the search term row will update to a queued icon, to show which terms you have already processed
Repeat the above across multiple search terms and tabs - adding more to the queue
Submitting the queued Actions in a single submission once completed, but pressing the 'Submit' button
The queued icons will swap out to a green tick, to show they have been submitted
Here are some more search articles to help: