Your macOS computer is behaving unstably. While it is booting, you press the Command+R keys and enter Disk Utility. Which Disk Utility option checks and fixes the filesystem?

The Disk Utility option that checks and fixes the filesystem is First Aid.
To run First Aid, follow these steps:
- Start your Mac in Recovery Mode by pressing and holding Command + R while it starts up.
- When you see the macOS Utilities window, select Disk Utility and click Continue.
- In the sidebar, select the volume that you want to check and repair.
- Click the First Aid tab.
- Click Run.
First Aid will scan the volume for errors and attempt to repair them. If First Aid is able to repair the errors, you will see a message that says "First Aid repaired the volume." If First Aid is unable to repair the errors, you will see a message that says "First Aid was unable to repair the volume."