How does the development of case law (court decisions) define the speech rights of public employees?

People who work for the government do not lose their rights because they work for the government. For example, public employees still have free speech rights in certain situations. The Supreme Court has reinforced this.
The Supreme Court has ruled that public employees have free speech rights on issues that deal with “public concern.” The Supreme Court, however, has not allowed unlimited freedom of speech for public employees. The case of Pickering v Board of Education set this concept in motion. If a public employee is speaking on a matter of public concern, the employee can’t be disciplined or fired for doing this. The Supreme Court believes that public employees are often in the best position to point out issues that may exist in the government organization in which that person works. Examples of public concern include speaking about the use of school district funds, testifying before the state legislature, and criticizing government inefficiency and waste. If, however, a public employee complained about the salary and benefits associated with a specific government job, this is not considered to be a matter of public concern and wouldn't be protected by the First Amendment.
Court decisions provide guidelines for what is protected regarding the First Amendment rights of public employees.
https://employment.findlaw.com/wages-and-benefits/how-does-due-process-protect-a-public-employee.html

https://www.workplacefairness.org/retaliation-public-employees