RecruitingPhase 2Drug trialAvelumab and M1774 in ARID1A-mutated Endometrial CancerThe purpose of this research study is to see if the combination of study drugs avelumab and M1774 is effective and safe for participants with endometrial cancer. The names of the study drugs involved in this study are: * Avelumab (a type of human IgG1 antibody) * M1774 (a type of ATR inhibitor)