[2021] I can't find the registration key

after several years, all of a sudden, when starting the game, they ask me for the registration key of the game. I didn't buy a physical disc. and I do not remember whether the letter key preserved. Several years have passed. I have a permanent 2Step Verification
... why suddenly such a requirement? I can't start the game until I find my registration number? buy a new version of the game again after so many years of donate ?!