Venetoclax in Combination With ASTX727 for the Treatment of Chronic Myelomonocytic Leukemia and Other Myelodysplastic Syndrome/Myeloproliferative Neoplasm

Inclusion Criteria: * A diagnosis of an MDS/MPN "overlap" syndrome with \>= 5% marrow blasts (including monocytic blast equivalent in case of CMML). Hydroxyurea may be used to control counts up until the start of therapy * White blood cell (WBC) \< 25,000/mm\^3. Treatment with hydroxyurea is permitted to lower the WBC to reach this criterion * Age \>= 18 years. Because no dosing or adverse event data are currently available on the use of ASTX727 in combination with venetoclax in patients \< 18 years of age, children are excluded from this study * Eastern Cooperative Oncology Group (ECOG) performance status =\< 2 * Total bilirubin =\< 1.5 x upper limit of normal (ULN) (unless considered due to Gilbert's syndrome) * Aspartate aminotransferase (AST) (serum glutamic-oxaloacetic transaminase \[SGOT\])/alanine aminotransferase (ALT) (serum glutamate pyruvate transaminase \[SGPT\]) =\< 3.0 x institutional ULN OR =\< 5.0 x institutional ULN for patients with liver metastases * Glomerular filtration rate (GFR) \>= 30 mL/min/1.73 m\^2 * Human immunodeficiency virus (HIV)-infected patients on effective anti-retroviral therapy with undetectable viral load within 6 months are eligible for this trial * For patients with evidence of chronic hepatitis B virus (HBV) infection, the HBV viral load must be undetectable on suppressive therapy, if indicated * Patients with a history of hepatitis C virus (HCV) infection must have been treated and cured. For patients with HCV infection who are curr…