Does k6 supports testing for monolithic applications ? Where can I find the documentation for it
For testing monolithic applications, do you mean load testing a website (end-to-end testing), as opposed to testing APIs (components)? If so, the docs should get you started: How to Load Test a Website: The k6 Guide. You can still test at the protocol level (e.g. http), no need to test each component if not possible. The supported protocols are documented in the k6 docs: Protocols.
k6 also has the option to do browser testing: Get Started with k6 browser using k6 browser. The main use case for the browser module is to test performance on the browser level. Browser-level testing provides a way to measure user experience and find issues that are difficult to catch on the protocol level.
If you can further elaborate what/why you are not able to test in your monolithic application, we can further advice.
Cheers!