Malware on Macbook? How to scan or secure it

You do not need any anti-virus for macOS as it has its own built-in security (including a read-only system partition) among other preventions. There is a reason that Microsoft issues a daily Windows Defender anti-virus software update. Anti-virus software will not prevent you downloading adware and malware that may be infesting applications downloaded from non-original vendor sites. Avoid download aggregation sites (e.g. macupdate, etc.).

We usually recommend the free to use Malwarebytes for Mac when adware/malware is suspected. You don't need a subscription, it will keep working (manually) after the trial period, and can be removed from its Help menu. It will detect any adware/malware and remove it.

See also:

Effective defenses against malware and ot… - Apple Community