This is going to sound like a troll but I'm a long-time Java developer that hasn't written Java code in over a year because I've switched to Kotlin.

Practically speaking, I'd start with whatever stack your new employer already uses. Having a solid understanding of the existing components will give you a baseline understanding of what was chosen and why.

One framework that's caught my eye recently is Micronaut which is basically a simplified version of Spring with added benefits like using little to no reflection.