Yes. A short thank-you note is still appropriate if that is your normal practice. It should not become an apology, post-interview case correction, or attempt to relitigate your performance.

The note is simply a professional close to the conversation. Recruiters and interviewers know candidates have uneven interviews, and a polished email rarely changes the formal evaluation either way.

Thank the interviewer for their time and mention one specific part of the conversation you appreciated. Do not explain why you missed a calculation or attach a corrected recommendation.

Send a brief note if you would have sent one after a strong interview. Then move on to the next process rather than trying to repair the case by email. The interviewer should be able to see what you would actually do next, not just hear a general principle.

A thank-you note should not become a post-game case correction.