The purpose of this study is to determine the recommended Phase 2 dose(s) (RP2D\[s\]) of JNJ-69086420 in Part 1 (Dose Escalation), to determine safety and preliminary signs of clinical activity at the RP2D(s) in Part 2 (Dose Expansion), to determine safety of JNJ-69086420 at the RP2D(s) as a combination therapy in Part 3 (combination therapy) and to determine safety of JNJ-69086420 at the RP2D(s) in participants with metastatic hormone-sensitive prostate cancer (mHSPC) in Part 4.