To be fair, almost all of the keyword-ish things Java's added have been done such that they rarely can change the meaning of any existing programs. Assuming I didn't miss any, all the keyword-ish things which have been added, ever:

  Java 1.4, 2002: assert
  Java 1.5, 2004: enum
  Java 10, 2018: var
  Java 14, 2020: yield
  Java 16, 2021: record
  Java 17, 2021: permits, sealed

Almost all were added in such a way that the extent of the breakage would be that a program which previously worked would now fail to compile (i.e. fail safely.)

(The only exceptions I can see are for `assert` and `var`, and even then only when some parts of a program are compiled with older versions of the compiler, and even then only when various other conditions are met.)