Replaced w/ what card? Be specific. Brand, model, specs, etc.
As previously suggested, you need to revert to a version of Mac OS supported by your 2009 iMac (w/out OCLP involved). Eliminate all those 'upgrade' variables. If the installed WiFi card doesn't work on a supported version of Mac OS then it's either the card or an issue w/ the logic board.
Have you tried resetting PRAM or SMC on boot?
Learn how to reset NVRAM, PRAM and SMC on Intel Macs, and what Apple silicon Macs do differently. Includes model-specific troubleshooting steps and when resets actually help.
www.macworld.com