Yes, it's the Boot Picker what I'm trying to get it to work. I've tried cmd-R, cmd-option-P-R, option, shift.
Unfortunately, I don't have any SATA PCIe card.
Thank you so much for taking the time and explaining all this to me. I really do appreciate it! I didn't know about the change of GPU card affecting these unsupported MacOS releases either...!!
Also, thank you for the price of the BootROM reconstruction!
I have my Mac Pro to make music, I have some new software that is for MacOS 10.15 or higher. That's why I wanted to update my Mac Pro. But I don't have the energy to take such great care of my computer, when it gets this technical. I guess I'll use my MacBook Pro that supports Catalina and make a network between them and that's it. But, if I do that, it still concerns me not being able to have any Boot Picker working though.
Many thanks again, Tsialex!