Oh, yes, Jon. I definately agree. I was sort of thinking aloud since the OP believes that a belief in ghosts is from the OT. I’m just not so sure. Neither am I sure that the proposition is supported by the Book of Samuel but, rather, a way of Saul recalling what was predicted would happen to him soon.
As to Bible (OT), we all can point to examples in the OT which The Church does not follow.
However, I think of the First Commandment, especially the part of having other gods before Him is the answer.
To me, a belief in ghosts places a power somewhere else other than what is in God’s power alone to do or allow — until or unless the Church validates the existence of a ghost of other presence which, I understand, they rarely do.
I should add here that my grandmother, a most devote Catholic, did believe in “ghosts” but in that case she was speaking of souls in Purgatory who were in need of prayer.
Maybe “ghost” is too generic a term.