In order for you to play Team Fortress 2 on macOS with minimal graphics settings, your computer must meet the following requirements
Operating System:
OS X version Leopard 10.5.8 and above
Processor (CPU):
1.7 GHz Processor or better
Memory (RAM):
1 GB RAM
Graphics Card:
NVIDIA GeForce 8 or higher, ATI X1600 or higher, Intel HD 3000 or higher
Network:
Broadband Internet connection
Storage:
15 GB available space