A Study of JNJ-95804306 for Relapsed or Refractory Hematological Malignancies

Inclusion criteria: For Arm A: * Have a diagnosis of: Acute myeloid leukemia (AML) per International Consensus Classification (ICC) 2022 or myelodysplastic syndromes (MDS) per world health organization (WHO) 2022 classified as moderate high, high, or very high-risk per the molecular international prognostic scoring system (IPSSM). All participants must have relapsed or refractory disease and have exhausted or are ineligible for standard therapeutic options * Body weight greater than or equal to (\>=) 40 kilograms (kg) * Eastern cooperative oncology group (ECOG) performance status of 0 to 2 For Arm B: * All participants must have relapsed or refractory disease with no other approved therapies available that would be more appropriate in the investigator's judgement. Have a diagnosis of either: Chronic lymphocytic leukemia (CLL)/Small lymphocytic lymphoma (SLL) meeting 2018 International workshop on chronic lymphocytic leukemia (iwCLL) National cancer institute (NCI) working group guidelines (Hallek 2018) that meet the following criteria: a. Participants must have received at least 2 prior lines of therapy; b. Have clinically measurable disease * Body weight \>= 40 kg * ECOG performance status of 0 to 2 * Must sign an Informed consent form (ICF) * For US sites: Have a diagnosis of CLL/SLL that meets iwCLL, NCI Working Group Guidelines which is relapsed or refractory and requires treatment with no other approved therapies available that would be more appropriate in the investigator's judgement. a. Participants must have received at least 2 prior lines of therapy Exclusion criteria: For Arm A: * Has acute promyelocytic leukemia according to world health organization (WHO) 2022 criteria or known active central nervous system (CNS) involvement of AML/MDS, unless in specific cohort (s) per study evaluation team (SET) decision * Need for supplemental oxygen use to maintain adequate oxygenation * Have evidence of uncontrolled systemic viral, bacterial, or fungal infection. Antimicrobial prophylaxis is permitted * For US sites: Has acute promyelocytic leukemia according to WHO 2022 criteria or known active CNS involvement of AML/MDS For Arm B: * Need for supplemental oxygen use to maintain adequate oxygenation * Have evidence of uncontrolled systemic viral, bacterial, or fungal infection requiring initiation of parenteral treatment as medical intervention * Developed Richter's transformation or prolymphocytic leukemia * Known active CNS or leptomeningeal involvement of CLL/SLL/Non-Hodgkin lymphoma (NHL)