The purpose of Part 1 (Dose Escalation) of the study is to assess the effective dose (recommended Phase 2 dose\[s\] \[RP2Ds\]) that can be safely administered, and dosing regimens of JNJ-90189892 in participants with relapsed or refractory (R/R) acute myeloid leukemia (AML) or R/R higher-risk type of myelodysplastic neoplasms (MDS \[type of cancer of the blood and bone marrow, which does not respond to treatment or comes back after treatment\]). The purpose of Part 2 (Cohort Expansion) is to further assess the safety, tolerability and efficacy in participants with R/R AML or higher-risk types of MDS at the RP2D regimen(s). The purpose of Part 3 and 4 is to assess the effective dose (recommended Phase 2 combination dose \[RP2CD\]) that can be safely administered, and dosing regimens of JNJ-90189892 in combination with azacitadine (AZA) + venetoclax (VEN) in participants with R/R AML (part 3) and newly diagnosed (ND) AML (part 4).