Why? Java 11 is already leaps and bounds better than Java 8.
I'm not sure that it's inherently insecure, there is just a ton of old stuff in the ecosystem still chugging away.
(For Java 9/10/11 in particular, there are several small enhancements, but nothing as earth-shaking as the changes we got with Java 7/8.)
And even in the unlikely event you don't see any improvement with recent versions of the runtime, something like Spring Boot 3 requiring Java 17+ isn't exactly "invisible" in the Java world.
7 didn't introduce anything earth-shaking (just try-with-resources), lambdas were earth-shaking, just like records and switch expressions are.