I have a 2012 mini, and Ventura is working fine. Wifi has no apparent issues while I am using it (sometimes several hours per day.) I would try a and rebuild of OpenCore. (Fixed some issues when I first updated to Ventura.)
I was reading that the 2012-2019 minis antenna worked better if the mini is stood up sideways. Seemed to help a bit but could be placebo. Now that Big Sur 11.7.3 is out I will update that and rebuild opencore to see if that helps. Just a keyboard hooked up to usb.