My usual disclaimer: interpretations of Kant vary in the scholarship. I don't think there is one super agreed-upon way of reading Kant (see: Korsgaard, Christine M. 1985. "Kant's formula of universal law." Pacific Philosophical Quarterly 66, no. 1-2: 24-47).

That said, you have to make sure first of all that you aren't reading Kant as a rule-utilitarian (which is a common mistake). For instance, many people apply Kant's universalization formula as follows: Imagine if everyone did that. Would that be a world that was desirable? If not, then it fails the test.

That is an incorrect reading of Kant (that's something all Kant scholars could agree on). Rather, it's that if the law, when universalized, would lead to a contradiction.

Now, the question is, "What does Kant mean by a contradiction?" Well, that's where the interpretations differ. That Korsgaard citation defends on interpretation and quickly goes over some of the others in the scholarship. Korsgaard chooses to defend what's called a "practical contradiction interpretation". Here, some act (or maxim of action) is contradictory when it is practically self-defeating.

We might imagine a world where people never lend their cars to their friends because they knew the cars would never be returned. In result, the maxim "To steal/keep a car that I ask to borrow and promise to return" would lead to a contradiction, since it would lead to a world/effect that would undermine the very purpose of the maxim: namely, to acquire cars. So, it is in some sense irrational to follow such a maxim since it brings about the opposite of its purpose. It is, in that sense, a contradiction.

I'm assuming, if you didn't take the rule-utilitarian route, that that is the kind of contradiction you're imagining. (You didn't write much, so I'm kind of in the dark, here.) And you're suggesting that almost every action would be self-undermining under such an interpretation, leading to a prohibition of "any action".

Imagine something like helping other people when they're in need. It's not clear how if everyone helped someone else out when they were in need, that this would be self-undermining. Or, imagine walking around. Merely walking through the park is surely permissible. And we can imagine everyone walking around without any kind of practical contradiction.

Perhaps you could tell me, more specifically, what you had in mind?