When looking at the technology tree, you find fairly quickly that you will need anywhere from 5 to 500 progenitor technology fragments. You get the 5 easily enough when you take the mission to unlock the Andromeda-Decay gate but after this you will need a little more information. My experience is rudimentary but I'll record what I have in the hope that the more experienced players will show us even more.

Progenitor Interface. In doing the mission to progenitor space you are instructed to locate the Progenitor Interface and these should show up as a lavender (?) chevron when you reach a dead planet in a D2 system. Unlock each of the 4 levers on the interface and an armored gigas will spawn and, assuming you prevail, will leave you anywhere from 2 to 3 progenitor tech fragments. I have no shame in cheesing more than one interface since it is a fairly reliable source of fragments.

Obelisk. These can either be anchored to a pedestal or levitating about 100 meters off the surface. If anchored, there is usually a rectangular opening on the upward ledge of one side of the pedestal and you drop down to get 2 to 3 fragments from the cargo box. If levitating, there is usually a triangular opening in the midsection on one side of the obelisk and this will reveal a container with again 2 to 3 fragments. Both pedestal and levitating obelisks can also be damaged in the midsection and this typically means that the cargo container is in an opening in the peak. Obelisks can appear as individual, paired or in a multi-member henge arrangement. The henge structures are usually guarded by groups of very territorial desert gigas so come prepared.

Unknown Structure. This is a ring stack that features a small rectangular entryway on the lower slope of the structure. While hard to see, when you find one you simply have to adjust your altitude to get the other 3 since they will be on the same axis. Inside the structure you typically find one to two containers with ancient relic and/or technology artifacts that a valuable items if you find a buyer. But if you are persistent you will also come across a cargo box either on the floor or connected to the ceiling of the structure. The floor variant provides 2 to 3 progenitor tech fragments while the ceiling variant can provide upwards of 10. Good times.

Dyson Sphere. For those rare players, actually completing the Dyson Sphere mission will net 20 progenitor tech fragments. I am not one of those players.

The dead planets feature many PoI like the Arcade, the Nexus and the Azure Nexus but I have not managed to find any artifacts in them. If other players have had better luck, please share that experience with the rest of us.

Enjoy