Further to that, the act of testing or observation isn't itself without its effects.
Let’s say this is an actual real phenomenon for sake of the discussion. Demonic possession and successful exorcisms would underscore the reality of the faith. The exorcist has a duty to the mission that they are given—the have a job to do recording viral video may not be part of the job description. The Catholic Church may not want evidence of this supernatural moment recorded or being supernatural, perhaps it can’t be for some reason. Maybe just the disclosure of it is enough by a priest to motivate some folks who would be motivated by such a thing to join the faith.
If it’s not real, well that last sentence above serves the same purpose, doesn’t it?
And besides…would you trust any video, audio, or photographic evidence of anything in 2023? I know I wouldn’t. It would be picked apart, ridiculed, and drive more people away from the faith than drive to it.