According to Wikipedia:
During a December 2017 test of various anti-malware software carried out by AV-TEST on Windows 10, Windows Defender earned 6 out of 6 points in detection rate of various malware samples, earning its "AV-TEST Certified" seal.
During a February 2018 "Real-World Protection Test" performed by AV-Comparatives, Windows Defender achieved a 100% detection rate of malicious URL samples, along with 3 false positive results.
An AV-TEST test of Windows Defender in October 2019 demonstrated it provides excellent protection both against viruses and 0-day / malware attacks.
On December 1, 2021, AV-TEST gave Defender a maximum protection score of 34 points after successfully managing to detect ten out of ten ransomware samples in a lab test.
Minutus cantorum, minutus balorum,
Minutus carborata descendum pantorum.