Hi Rupendra Sharma
Good day!
Welcome to Freshworks Developer Community!
I tried adding the same nodemailer dependency to my app in local and it installed successfully.
FDK version - 7.3.0.
Node version - v12.22.9 and v12.18.2
Can you try upgrading to fdk 7 and try again - FDK v7.0 - Announcing Node.js v12 and ES6+ support.
Another solution that seems to have worked for many - https://github.com/nodejs/help/issues/2874