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This is a very theologically imprecise statement and is the root of your errors. You need to do more research about +Bellarmine.  "Manifest heresy" does not mean what you think it does.  It is a canon law term; it does not mean that some "sounds/acts like a heretic".  "Manifest" in this case, does not mean what the dictionary says it means.  It implies perniciousness and other legal aspects.
.+Bellarmine used the term "manifest" before the material/formal designations were invented.  Over the centuries, various theologians have used all kinds of words to describe the MULTIPLE levels of error, schism and heresy.  You can't just pick a term and use it out-of-context.  If you want to use the term "manifest heresy" correctly, you need to research when and how it was used and then correlate that to when/how the modern terms are used (i.e. material/formal).  That's assuming you want to have an intellectually accurate conversation.  As it is now, you are just using a term haphazardly, and incorrectly.  It's lazy, theologically wrong and (since you're using the term to condemn others) it's uncharitable.

+Bellarmine used the term "manifest" before the material/formal designations were invented.

Neque cuм liber definitur haereticus, definitur eo ipso quod
auctor fuerit formaliter haereticus: poluit enim imprudenter errare.

A manifest heretic may or may not be a heretic. The point is: I should act as if he was one.

What???  A "manifest heretic may or may not be a heretic"?  That's a self-contradictory proposition.  Please take a Logic 101 class and check back in with us.  If you find a particular OPINION or POSITION to be erroneous, then by all means, reject the position, but otherwise you may certainly not act as if he were one.  It is not for you to arrogate unto yourself the authority to determine who is and is not a Catholic.  So if you were a priest, you'd consider yourself entitled to refuse Vigano communion if he came to receive?  And "manifest" to whom?  To you?  It's manifest to YOU that he's a heretic, but it's not manifest to most Catholics.  So he loses membership in the Church based on your own private judgment, however insane and unhinged it might be?

It sounds like you're using the term "manifest heretic" as meaning someone who is suspect of heresy.  That is not how St. Robert Bellarmine used the term, since he declared that manifest heretics lose membership in the Church.

For although Liberius was not a heretic, nevertheless he was considered one

they judge him to be a heretic pure and simple, and condemn him as a heretic.