MacBook is attacked but can't find any threats
"Going slow" is not really an indicator of malware. Most malware can do its job without using significant CPU, and malware designers want their software to be unnoticed.

If several malware apps have said "it's not malware", then that's probably true.

It's much more likely that there are other problems with your Mac. Check Activity Monitor, and see what is using excessive CPU. Remove third-party Launch Agents or any other software that runs in the background. Test a new user account, and see if that it better. If so: it's a user account problem.

Make sure you have low memory pressure (also in Activity Monitor), and that you have plenty of free disk space.