(1) P → Q
"If the object of a knowing is an appearance, then the knowing is filtered."

(2) R → ~Q
"If the object of a knowing is an action, then the knowing is unfiltered."

(3) R → ~P
"If the object X of a knowing is an action, then X is not an appearance."

You were on the right track: like a modus tollens but there's a condition hanging over it in (2).

What does it mean to know my action in an unfiltered way? If I serve up chicken and in serving up chicken I unknowingly serve up salmonella, then I know my action of serving up chicken and I do not know my action of serving up salmonella. There is an action of my own that I know and an action of my own that I do not know. They may or may not be the same action. If they are different actions then they are not different in the same way as the action of serving up the chicken is different from the action of pouring the wine. What is filtering and where does it fit into that account of actions of my own which I know or do not know?

The OP argument may be invalid on account of premiss two (and perhaps others) not having a clear or coherent meaning.

'P' for 'is an appearance'

'F' for 'is known in a filtered way'

'U' for 'is known in an unfiltered way'

'r' for 'our action'

(1) Ax(Fx -> ~Ux) premise

(2) Ax(Px -> Fx) premise

(3) Ur premise

(4) Therefore, ~Pr

That's valid.

You left out the premise Ax(Fx -> ~Ux). In other words, you did not make explicit that if something is known in a filtered way, then it is not also known in an unfiltered way.

(2.) We know our action in an unfiltered way. — KantDane21

(2) equivocates "our" in meaning. Not all action can be known. My action may or may not be filtered to me but other actions are always filtered.

It's not about going into the meanings of "appearance", "filtered way", "unfiltered way", or "our action". Rather, it's about the logical form, no matter the meanings of those are.