TF2 won't actually run on a system like that, the system requirements on Steam are a bit of a meme. It's 18 years old but it's also been updated for 18 years.
If you open "properties" and then "Betas" in Steam, you can download old 32-bit versions of TF2 and play on dedicated servers. There's also a recompile of the leaked source code available, so I think 32-bit clients with a TF2 addiction will be okay for a while longer.
