Updated iMac to Big Sur and now cannot connect it as external monitor to MBP

I updated my 2014 iMac 27" to Big Sur, and now I cannot connect it to my 2016 MBP(running Catalina) as an external monitor. I tried command+F2 and nothing happens. There is no option for external display options on my MBP either. I have connected the iMac as an external before using different OS on each computer. Is anyone else having this problem, and is there a fix for this?