He gave lectures and wrote essays and they contained remarks about being bullied online, and about how it messed with his psychy. What comes to mind as concrete example is his essay: Exiting the vampire castle.
Fisher had a depression that likely has been caused by "capitalist realism", and in addition he was hounded by online cancel culture, which drove him over the edge. It's an ideological question whether that counts as a suicide or murder.
If you are a materialist you will consider the psychologically detrimental environment of late stage capitalism as the likely cause for Fisher's depression. The people that harassed him online are considered responsible for his death. The guilt should be split between Twitter and his cyberbullies. Psychological damage is not immaterial, brains are physical organs.
The neoliberal ideology says that the environment has no effect on people's brain and claims that depression is caused by a chemical imbalance, which is treated as a first cause. Which is a logical error, statistically speaking there is an astronomically low probability that brains just popped into existence fully formed with a chemical imbalance. It's an ideological mechanism to convert any kind of systemic criticism into a personal flaw of the person that does the criticising.
The speculation that he could have been targeted by a psyop is not far fetched, after all marginally leftist activists like Aron Schwartz are confirmed to have been driven into suicide. The Software developer Ian Murdock the founder of the Debian operating system was driven into suicide according to his suicide note. And the ability to do psychological torture is also well documented. It's not unlikely that the idealogical enforcement apparatus of the neoliberal hegemony would try to kill off vulnerable opponents by weaponizing social media.
A categorical dismissal of conspiracy theories is unreasonable, because it contains an indirect assumption that powerful people do not conspire to hold on to power. That would make you a coincidence-theorist. We should consider to weaken the assumption of innocence for powerful people because very few people become powerful by innocent means. It's unknown to me that Fischer was a target of a psyop but it's not unrealistic that he could have been targeted as a vocal critic of the neoliberal ideology. Post too long. Click here to view the full text.