Qualtrics.SurveyEngine.addOnReady(function () {
    let qc = this.questionContainer;
    let all_na = qc.querySelectorAll(".last");
    all_na)3].hide();
});
Add this code to your js.
The

.last

all_na 

Hi AhmedA,
Thank you very much it works perfectly well! :)
Regards,
Houston

Thanks for this good answer.

I wonder how can I select not just the last column to hide, but all columns save the first column?

In my case the N/A is the last row, not a column. That's because I need n/a as a question item for the user to indicate the entire question is not relevant for them. I therefore want to hide the answer columns for the n/a row, except for one column (the columns are frequency, so it doesn't make sense to fill out a frequency for the n/a item in my case).
I managed to hide multiple columns this way:
Qualtrics.SurveyEngine.addOnReady(function () {
  let qc = this.questionContainer;
 // console.log(this.getQuestionInfo());
var all_na = new Array();
var columns = s".c4", ".c5", ".c6", ".c7"] 
for (let i = 0; i < columns.length; i++) {
  qc.querySelectorAll(columnsci])m10].hide();
  };
});

However now the n/a question item no longer works as an exclusive item. Any idea why?

https://community.qualtrics.com/XMcommunity/discussion/comment/51815#Comment_51815elephantus
Don't use the hide function use the below style property. It will keep the exclusive property intact. You can change the column id's as needed.
 qc.querySelectorAll(columnssi]))10].style.visibility="hidden";
Hope it helps!

elephantus ,
In the last row, hide all but last column (regardless of number of rows or columns):
Qualtrics.SurveyEngine.addOnload(function() {
jQuery("#"+this.questionId+" .ChoiceRow").last().find("td").not(".last").find("*").hide();
});

https://community.qualtrics.com/XMcommunity/discussion/comment/51818#Comment_51818Thank you Deepak! That indeed works. What is frustrating is that the behaviour of exclusivity is for the same column only - and not for all columns. So in other words, I would like it when a specific answer choice is chosen, that it deletes any other choices made in other options across all columns in the matrix.

Thank you

https://community.qualtrics.com/XMcommunity/discussion/comment/51830#Comment_51830elephantus You can implement click function on the below code for just the last row options and use the code mentioned in this link to reset all radio button.
Qualtrics: Reset Likert Matrix. Works with single or multi-select matrix. Add button html to question text. #qualtrics #js #jq #matrix #likert #reset · GitHub
Hope it helps!