OK so I completely suspect this is me but here is the issue. I have an old cheesegrater Mac Pro that has served well and is now running Mojave. I am reticent to move on to Catalina due to software that I use . the issue occurred when I decided to install Windows on an SSD and shove it into the mac pro as an optional boot drive as Parallels was frankly too slow… It works fine but when put in it will only boot to Windows. I have bought a copy of bootrunner thinking it will solve the issue but the log in screen only comes up when I don’t have the windows SSD shoved in. So I know bootrunner works as I have disabled the autolog in on OSX and it appears and gives me the option to boot into osx and thats great however it does not appear when I have the windows disk put in as well. Note I installed windows with all the other drives removed as it refused to allow me to use bootcamp.
MacPro 2009 now running 2x 3.46 Xeon and a vanilla PC Radeon RX Vega 64 with OSX on an PCIe drive
so yes it has been tweaked but as I have been disabled for the past 14 years I need to keep it going for as long as possible and it has been a trusty companion. Any advice very gratefully received, many thanks . I do have winclone pro so would try to take windows off the ssd when connceted by usb ( as I cant get to osx when it is in the computer) but not sure if that would help in any way.