Need Help IF POSSIBLE

I have a really good Dell Optiplex 3060, i5 8th generation (coffee lake I believe), with a 1Tb SSD, everything else is virgin on the MB and the rest of the box from dell.

I tried to convert this into a HT, using mostly every youtube video, and opencore help and I have no idea what else, but I can't make it work, I cannot even get to the point where I can format the SSD, I am literally trying to do something I have never done.

I am not sure if this is the correct place to ask for help, but hey, I have 2 possible answers and 1 of them is yes, so I have nothing to lose and a lot to gain.

I am NOT interested in Big Sur, I want to stick with Catalina.

Is there anyone that can help me out pointing me towards the right instructions?

Any help will be appreciated.

Harold.