Experienced Java/Kotlin developers: what libraries do you use in your day to day work?

I am going to start my new job as a senior developer soon. New company primarily Kotlin/Java/MySql/Dynamo. (They don’t use Spring.)

Problem is all my life I have only done Python and a bit of JS. So I was wondering if there are any common libraries that I should try beforehand?

Couple that I could find are OkHttp and Retrofit. Am I even close?