All OSes have vulnerabilities, and the thing is MS Defender is a working solution that prevents many attacks. Microsoft also has to provide some nominal support to enterprise apps that are 30 years old, because that's a significant amount of what keeps them in business. Patching actual root causes would often mean changing the way things work at a fundamental level in the OS, and would break apps for a lot of their users. This could create a big problem for a lot of people.

Don't worry about it too much, this meme is just garbage and basically everything it asserts is wrong or inaccurate. The other person who replied to you was just being a condescending smuglord because you asked reasonable questions instead of participating in the "Windows Bad" circlejerk.