Running an outdated OS like Yosemite and older software versions leaves your system vulnerable to security risks. It is best to keep this machine offline if possible.
Currently, the official FL Studio Download Page lists macOS 10.15 (Catalina) as the minimum requirement. fl studio mac os x yosemite download
For OS X Yosemite, your best bet is for macOS. This is the final 32/64-bit hybrid version that officially supported 10.7–10.10. Running an outdated OS like Yosemite and older