The term 'materialism' includes the idea that everything that exists is composed of physical matter and energy including consciousness. This term is a philosophy intended to exclude belief in spiritual or non-physical realms. We have had this debate a few times before and your expanded view of materialism is not what the term was created to mean.
It's not how YOU use the term, but you aren't some sort of authority on the proper use of "materialism".
There's a long history - that you choose to ignore - that defines anything that interacts with matter as material itself. IOW, if ghosts could interact with matter in any way whatsoever, then ghosts would also be material.
Of course, the line between "material" and "immaterial" tends to shift over time based on available evidence: "immaterial" things that are well-established becoke "material". This lets the dualists keep up their claim that materialists never accept the existence of the immaterial. We do, of course; it's just we accept it when it's established that it actually exists.
I, of course, strongly disagree.
... right now. Other times, you've acknowledged the poor quality of evidence for ghosts by making excuses for why it's poor and criticizing those who ask for the evidence for ghosts to meet a reasonable standard.
That is because some people believe Nessie is a physical animal, hence something that would not contradict the materialist philosophy. If they claim that Nessie is a ghost that sometimes materializes then that would contradict the materialist worldview.
How so? Plenty of physical phenomena materialize and dematerialize. Why would that make Nessie immaterial?
... or are you just begging the question by slapping the label "ghost" (which you've conveniently defined as something immaterial)?