Okay, I managed to scour some information about the TF2/CS:GO leak, talked to few people and gathered the following:

1. This is an OLD LEAK. Supposedly the archive file shared on some places is named "April 22 2020", but the files are from a 2018 leak, VALVe knows about this

2. As far as it is currently known - there are no remote execution exploits possible. There are rumours going around, but nothing has been proven yet.

3. Steam is safe, there is no Steam code. The source code for the games are leaked, not Steam.

I know devs were most concerned by this one.

That is all I gathered with some degree of trustworthyness

At a time like this, a lot of rumours and a lot of lies float around, so take everything you read with a grain of salt INCLUDING THIS THREAD.