It's the other way around.
The mental illness is not "paranoia about Trump's doings", paranoia about Trump is normal when you're a decent human being who is thinking clearly and fact-based, because then you should absolutely be paranoid about an unhinged, mentally unstable, dangerous fascist taking power in the US. If that doesn't bother you, I'm sorry, but you're probably simply uneducated. See old Nazi Germany for "prior art" on this one.
What could be considered a "mental illness" is what causes people to believe or support Trump, or the current Republicans, or the MAGA movement, or the current right-wing extremism in general. This is likely an issue of either low education, low intelligence or naive belief in various forms of internet propaganda. Or multiple of those issues combined. So it's not really "illness" but rather a misinformed and/or radicalized person. Similar to what cultists become in real cults. Fascism is very cult-like in general. There's usually a supreme leader and a doctrine (usually based on falsehoods) to live by, and everyone who doesn't do that is considered an "enemy" or at least inferior. What you read on the internet and especially social media or "alternative news sites" is already often weaponized and might be able to radicalize you or lead you away from the fact-based truth. There's TONS of disinformation, sometimes harmless, sometimes funny, but sometimes not. Sometimes it's dangerous, especially if you're not able to spot what's likely true or not. If you aren't able to filter out disinformation, propaganda, lies, half-truths, weird memes, i.e. if you are unable to stick to reputable sources, peer-reviewed science, and so on, then you WILL fall for at least some amounts of misinformation and you MIGHT even become part of a cult (e.g. MAGA movement, conspiracy believers, anti-vaxxers, QAnon, radical right-wing extremism, ...). And again, it's all weaponized and that is useful for various involved parties for various reasons. For example, Putin wants misinformation on social media because with it he can destabilize Western democracies, because common citizens fall for this stuff and lose faith in their own governments. The end result helps Russia, because Western democracies will then do less and be less united against Russian attacks. Billionaires like Musk or Zuckerberg want misinformation on social media because with it they can better control the narrative and extract more money from the users because polarizing and extreme content gives them more interactions and thus money. Billionaires also want less governmental regulation, which is why Musk already demolished several regulating bodies in the US. Autocratic fascists like Trump also want misinformation on social media because with it they can control the narrative better. What these involved parties all don't want is the actual truth, so they are usually anti-science, anti-education, anti independent journalism, and so on. It's better for them if the common people are uneducated and uninformed, and follow the newly created doctrine. It's easy to tell that they want to create their own fake version of the truth, and control the narrative in that way.