Someone signed into my apple ID with 14 length ramdomly generated password

This is the 7th time I got an email saying that someone signed into my iMessage by some unknown person since May this year. 3 times by datadriver’s Mac, 1 time by lijy的Mac, then another 3 times by macen的iMac.

I changed my password multiple times already, and this time had my password changed to 14 length password created on bitwarden, with special characters, numbers, and capital letters. And yet, another email saying that someone signed into my iMessage. There are a lot of people having similar problems as you can see in this reddit post: https://www.reddit.com/r/applehelp/comments/bfl7d5/has_anyone_ever_experienced_an_unauthorized_apple/?sort=new

Is this Apple's problem? or something I am doing wrong? Is there any solution to this other than 2FA?