Spawning blocks are very important in a gold farm because they effect what mobs spawn in your farm. If you have piglins that don't drop gold and hoglins in your farm then it will obviously produce less gold per hour than if you just had pigmen. There are a few common spawn blocks. The most common of these is magma blocks because it spawns only pigmen and magma cubes. Magma isn't accually the best option though but I will discuss that in a little bit. Netherack on the other hand is extremely easy to get because the entire nether is made out of it but anything can spawn on netherack. The most efficient option is soul soil that is lit on fire. The reason this is better is because like magma only pigmen and magma cubes spawn but if a pigmanspawns on a chicken the pigmen won't aggro towards you til the chicken dies. Therefore the fire kills the chicken faster and makes it ever so slightly more efficient. Now this is kind of a pain to have to farm soul soil and then light it all on fire so if you really wanted you could ust use magma blocks.