Is it good idea to make a "Fetch" calls from User event's injected HTML to NetSuite Suitelet? or will it case any issues??

Fetch calls from injected HTML to Suitelets can work but may lead to CORS issues and authentication problems. The injected HTML runs in a different context than the server-side script. This makes session management complicated. A better approach is to handle data processing within the User Event script itself. Alternatively, use client scripts with the N/https module for API calls that remain within NetSuite's security context.