Secondary research or desk research is a research method that involves using already existing data. Existing data is summarized and collated to increase the overall effectiveness of the research. Secondary research includes research material published in research reports and similar documents. The data points, although they are existing, are not easily accessible. Either they are highly-priced, or need some kind of subscriptions and so on.
These are some of the hacks which I personally use when I do secondary research and trust me these hacks work like a charm!

1. The "Case Studies aka Customer success stories"
Let's start with the basics, "What is a customer success story?"
Customer stories usually go into further detail on how the outcomes were obtained and what compromises were made along the way. A customer tale that can be thought of as a means to provide the intended audience with a "sneak look" into what might be their reality. This sneak peek provides enough information if you are conducting any secondary research, information in terms of impact in different KPI, such as revenue, customer acquisitions, lead generations, etc.
For example, Adobe customer success stories, Amazon (AWS) customer success stories, Hubspot case studies and many more.

These data points will help you to narrow down your solution, to guesstimate the trend and project the outcome of your solution with proper justifications.
2. Consultancy Reports - One for all, All for one
Consultancy reports are written for a non-specialist audience. Often they are written in response to a request for information from an organisation or business or just for the normal audience ( marketing strategy?). The best part of these reports are, they are FREE! and BEAUTIFUL! and EASY TO UNDERSTAND! and FULL OF INFORMATION!

These numerous firms conduct periodic surveys, on an organizational level, industry level or general and compile all the data into meaningful insight for the general public to consume it.
e.g. Deloitte Industry Outlook, (set the region before you access the reports to get more region oriented information)
3. Google Scholar - When Google is not enough
Google Scholar is a freely accessible web search engine that indexes the full text or metadata of scholarly literature across an array of publishing formats and disciplines!
Google Scholar aka the academic version of Google, will save the day by searching repositories of publishers, universities or scholarly websites rather than carrying out a generic web search. There are multiple filters available (not as robust as Google, but eh! something is better than nothing!)