The "real-time protection" built into macOS is better than anything that can be hung off the side later using third-party Utilities.
Malwarebytes makes it money from the Premium version, but the free 'disinfectant scanner' is the part you may need if you suspect a current infection. If you wish to support the developer, buying the premium version is one way.
Etrecheck presents a comparable dilemma. It can also detect malware (along with many other issues) with its free limited runs version, but asks you to purchase a premium version of you find it valuable, to support the developer.