Using "CleanMyMac" and "Microsoft Defender.

Those apps are neither required nor recommended.

CMM is regarded by many here, me included, as malware with the ability to arbitrarily mishandle user file data. I agree with @neuroanatomist's recommendation that you uninstall that app and don't install MS Defender.

Your Mac requires no always-on, third-party anti-virus or anti-malware software.

Apple has built these protections into macOS and they are updated regularly.

• macOS security built right in. - Apple Support   

• App Security Overview - Apple Support

Always-on anti-virus apps and cleaning apps often interfere with the performance and operation of macOS and are not recommended.  

An occasional “as needed” scan with the Malwarebytes app is likely all you will ever need. Malwarebytes is a popular tool among veteran users here in the Community. Run the app and see if it can identify any malware you may have accidentally installed. The free version is probably all you need at this point to identify and quarantine potential problems.

Load a few more unnecessary and too often problematic apps for best tangles, best performance degradation, and best added noise, and all for negligible or negative benefits over the built-in cleaning, and the built-in security.

If your organization requires Microsoft Defender or some other endpoint security, contact your IT group for support.

Add-on cleaner apps and add-on security apps and add-on “coffee shop” VPN apps are themselves too often sketchy, if not reminiscent of being actual malware, these days.

joop210 wrote:

I installed "CleanMyMac" on my MacBook Air 3. Is it possible to work together with "MicroSoft Defender" on the same MacBook.

Uninstall both of them right away. Rule 1 of Macs is don't install junk.

If you actually installed and used "CleanMyMac" you may need to completely erase the Mac and reconfigure it from the ground up. Uninstalling it, even when performed in strict accordance with its uninstallation instructions, is an ineffective remedy. The Mac must be erased.

Hopefully you created a Time Machine backup prior to installing it. Did you? If so all you need to do is to restore that backup: Recover all your files from a Time Machine backup - Apple Support

Best advice: uninstall CleanMyMac and don’t install Microsoft Defender.

I agree with the first two posters. CleanMyMac is well known for causing problems.

See also:

Effective defenses against malware and ot… - Apple Community

I would add that these apps are best removed using the vendor's uninstaller app.