This study involves taking a study drug called SAR443579. The overall goal of this study is to find out if the study drug is safe and effective at treating adults and children with relapsed or refractory acute myeloid leukemia (R/R AML), high risk myelodysplastic syndrome (HR-MDS), or B-cell acute lymphoblastic leukemia (B-ALL). This is a first-in-human research study.