If I have a list after a single gerund, do I use "is" or "are"?

Below is my sentence. I'm pretty sure the word "knowing" is a gerund, but please correct me if I'm wrong. I assumed that the only subject is "knowing" and that the linking verb should be "is", but grammarly flagged it. Is the sentence correct? Is grammarly wrong?

"I have found that knowing how to effectively manage and organize paperwork, requests, and deadlines is the only way in which to get the job done effectively."

Is grammarly reading the sentence like this?: "I have found that knowing how to effectively manage and organize paperwork, knowing how to effectively manage and organize requests, and knowing how to effectively manage and organize deadlines are the only ways in which to get the job done effectively." It seems like in this sentence, it clearly needs "are" for a linking verb (even though it's obviously a cumbersome sentence that nobody would write).

Is my original sentence correct???

Solution 1:

I have found that [knowing how to effectively manage and organize paperwork, requests, and deadlines] is the only way in which to get the job done effectively.

It's fine with singular "is". The reason is that non-finite clause subjects take singular verb agreement. Here, the large subordinate that- clause (in bold) functioning as complement to the verb "found" has the non-finite knowing clause (in brackets) as subject.