Because Mac OS X 10.6.8 does not support modern security protocols (like TLS 1.2/1.3), even if you found an old installer, it would likely fail to connect to WhatsApp's servers. Hardware Limits:

There is no direct free download of WhatsApp for Mac OS X 10.6.8 because the software never existed. Do not fall for scam sites. Install Roccat Browser and use WhatsApp Web—it is your only safe, free, and functional path forward.