There is a cheat/exploit discovered that allows someone (A human cheater, not bots) to effectively brick your copy of TF2, even through a reinstall. A cheater can disconnect you from a server and make it impossible for you to be able to re-launch the game ever again.

https://fxtwitter.com/BigChapAlien21/status/1796590661795545163

Play the game with caution. BigChapAlien21 can no-longer play TF2 because a cheater accused him of ping spoofing, when in reality their ping was low because they were on an Ethernet cable.

It is recommended to not play Casual or Competitive at this time.