RecruitingPhase 2Drug trialTrifluridine/Tipiracil + Oxaliplatin in Participants With Advanced or Metastatic Biliary Tract CancerParticipants are eligible for this study who were treated for advanced biliary tract cancer (BTC) but the treatment either did not make the cancer better or is no longer working. The treatment for patients whose advanced BTC either did not make the cancer better or is no longer working is a combination of chemotherapy drugs called FOLFOX which consists of fluorouracil and oxaliplatin. Studies have shown that other treatments may work better to treat advanced BTC. In this study, investigators want to see if treating patients with the drug combination of trifluridine/tipiracil (FTD/TPI) and another drug called oxaliplatin works better than FOLFOX for advanced BTC as second-line therapy. FTD/TPI are pills that are taken by mouth, whereas oxaliplatin is given intravenously (by IV).