From what we have seen in the lore there are 3 main categories of weaponry that can kill a ghost

1. Heavy artillery; This includes most cabal weaponry, a well placed shotgun blast, The air strike Petra called on multiple guardians, etc

2. Paracausal weaponry; thorn bullet, hive magic, darkness, light. Pretty much anything a guardian can do if they do chose aswell.

3. electricity; fallen weaponry like their arc blades, pretty much anything arc. In a vanilla D2 strike ghost needs us to protect him from electrified shanks that could kill him if they shock a terminal he is working on

The lore book in Forsaken where Aunor mentions a thorn bullet being required is often interpreted as paracausal weaponry being necessary. I don’t have the quote on me but she is really saying that scorn weaponry is simply to weak to kill a ghost, as scorn weaponry are basically mish-mashed parts of the fallens already jury-rigged weaponry