@CopperKettle's answer in the linked question is definitely relevant here. Quoted below:
"What makes her laugh are dirty jokes."
The meaning: We hear her laughing right now. We both know that she is laughing right now because she has just heard some jokes. I want to say to you that in my view the jokes she is laughing to are dirty.
"What makes her laugh is dirty jokes."
The meaning: When she hears dirty jokes, she usually laughs.
Some trustworthy-looking references are provided for this. I think this sounds pretty reasonable in terms of "strictly correct" grammar.
However, what I can say as a native speaker of American English is that the examples with "are" always sound wrong to me. When "what" is used as a pronoun, it is always singular. Note that the verb agrees with the subject, so when "what" is not the subject, the verb may be plural. For example:
What we are looking for is volunteers.
Volunteers are what we are looking for.
When phrased as a question, "what" does not function as the subject:
What are you looking for?
You are looking for what?
One of the things to recognize here is that you can say "[singular noun] is [plural noun]" or "[plural noun] are [singular noun]". It is not necessary for both nouns to agree. For example:
The thing I like most about France is the pastries.
Games are my favorite way to pass the time.