Google flags Immich sites as dangerous

As someone who doesn't like Google and absolutely thinks they need to be broken up, no probably not. Google's algorithms around security are so incompetent and useless that stupidity is far more likely than malice here.

Incompetently or "coincidentally" abusing your monopoly in a way that "happens" to suppress competitors (while whitelisting your own sites) probably won't fly in court. Unless you buy the judge of course.

Intent does not always matter to the law ... and if a C&D is sent, doesn't that imply that intent is subsequently present?

Defamation laws could also apply independently of monopoly laws.

Callous disregard for the wellbeing of others is not stupidity, especially when demonstrated by a company ostensibly full of very intelligent people. This behavior - in particular, implementing an overly eager mechanism for damaging the reputation of other people - is simply malicious.