> more than a month or something

6 weeks.

> But your employer can still check that you're actually sick.

Within limits, yes. Tesla in Germany went way beyond that though. Private detectives and managers showing up at employees houses to check they're actually sick.

They're also holding back the salaries of sick employees and are pressuring sick employees to give up their medical privilege and share personal health information with them.

Highly unethical and very likely illegal in some instances.