Probably some trojan or mallware you got from some p0rn site. Just kidding... But the method is the same. Either your keys were leaked, or you installed a compromised electrum wallet.
Or as i said, you have a STD on your pc that looks harmless, but is waiting for you to open your wallet
This is one of the options , no doubt about it. Although it seems to me that if the OP is a player, and gambling is conducted from the same device where he stored his seed phrases and passwords, then there is nothing surprising about where he could get a bunch of viruses from. Just one phishing link is enough; the RAT virus that was detected in him monitored all file openings. And the keylogger quickly transferred his wallet password to the right place. It is surprising that Windows, gambling, and finances for many still exist as something harmless, publicly available, used together, and in the literal sense.