We need more information to be able to piece together what happened.
The Bitcoin Core was running on what OS?
What were you doing around the time of the theft?
Bitcoin Core wallets are protected by a password, they don't use seed phrase technology but rely on some "hdseed" that's similar but will not be encrypted without a password. Therefore if the wallet file is stolen, it can be brute-forced for weak passwords.
Well, the hacker obviously got hold of the password... to be able to do that. Did you leave your computer running for extended times without watching it? (They could have installed keyboard logging tools and waited for you to leave the room and then logged in and transferred the funds)

The bulk of my "treasure" are stored off-line so I know that it will not be accessible .....and it is split into smaller amounts, so even if someone hack me, they will only get access to say 1% of my coins.
I also put out "bait" in the form of small amounts of coins in desktop wallets ...so if that is triggered, then I know I am being targeted.
Sorry for your loss.
