A Study of VX-121 Combination Therapy in Participants With Cystic Fibrosis (CF) Who Are Homozygous for F508del, Heterozygous for F508del and a Gating (F/G) or Residual Function (F/RF) Mutation, or Have At Least 1 Other Triple Combination Responsive (TCR) CFTR Mutation and No F508del Mutation

Key Inclusion Criteria: * Participant has one of the following genotypes: * Homozygous for F508del; * Heterozygous for F508del and a gating (F/G) mutation; * Heterozygous for F508del and a residual function (F/RF) mutation; * At least 1 other TCR CFTR gene mutation identified as responsive to ELX/TEZ/IVA and no F508del mutation * Forced expiratory volume in 1 second (FEV1) value \>=40% and \<=90% of predicted mean for age, sex, and height for participants currently receiving CFTR protein modulator therapy; FEV1 \>=40% and \<=80% for participants not currently receiving CFTR protein modulator therapy Key Exclusion Criteria: * History of solid organ or hematological transplantation * Hepatic cirrhosis with portal hypertension, moderate hepatic impairment (Child Pugh Score 7 to 9), or severe hepatic impairment (Child Pugh Score 10 to 15) * Lung infection with organisms associated with a more rapid decline in pulmonary status * Pregnant or breast-feeding females Other protocol defined Inclusion/Exclusion criteria may apply.