Defender reporting recipient email doesn’t accept long TLDs

When I try to set the IP Lockouts reports recipient to my email address @mydomain.tech, It appears that the email domain must be either 2 or 3 digits long. After that, it says “Invalid email address” and I can’t click to add it.
I tried .design and random TLDs as well as fake ones with 3 digits. All 3 digit addresses are acceptable and nothing more or less works.