Testing the Addition of an Anticancer Drug, BAY 1895344, to the Usual Chemotherapy With FOLFIRI in Advanced or Metastatic Cancers of the Stomach and Intestines

Inclusion Criteria: * For Dose Escalation: Patients must have histologically or cytologically confirmed advanced or metastatic gastrointestinal (GI) cancers with Response Evaluation Criteria in Solid Tumors 1.1 (RECIST1.1) measurable disease who have progressed on at least one prior treatment for metastatic disease and for whom FOLFIRI is considered a reasonable treatment option. Patients with mismatch repair deficiency should have progressed on immunotherapy * For Dose Expansion: Patients must have either: * Colorectal cancer who have previously progressed on irinotecan and tolerated an irinotecan dose equal to or greater than the recommended phase 2 dose (RP2D). If they have mismatch repair deficiency they should have progressed on immunotherapy OR * Gastroesophageal cancer who have progressed on at least one first-line therapy for metastatic disease. If they have mismatch repair deficiency they should have progressed on immunotherapy * For Dose Expansion: Patients be willing to undergo biopsies for research purposes only. The accessible tumor can be the primary or metastatic tumor site. Both research biopsies should be taken from the same tumor site * Patients must have progressive disease on at least first-line therapy for metastatic disease. Previous treatment with irinotecan is allowed * Age \>= 18 years. Because no dosing or adverse event data are currently available on the use of BAY 1895344 in combination with FOLFIRI in patients \<18 years of age, children are…