A Study to Evaluate TAR-210 Versus Single Agent Intravesical Cancer Treatment in Participants With Bladder Cancer

Main study only: Have a histologically confirmed diagnosis (within 90 days of randomization) of IR-NMIBC with at least one of the following criteria fulfilled: a. Ta low grade (LG)/ Grade 1 (G1): primary or recurrent, b. Ta LG/G2: primary or recurrent and c. Greater than or equal to (>=) 1 of the following risk factors: i. Multiple Ta LG tumors, ii. Solitary LG tumor >= 3 cm, iii. Early recurrence (less than [<] 1 year), iv. Frequent recurrence (greater than [>] 1 per year), v. Recurrence after prior adjuvant intravesical treatment (single perioperative dose of chemotherapy does not fulfill this risk factor)

Substudy only: Have a histologically confirmed new diagnosis (within 90 days of randomization) of IR-NMIBC for whom MMC is deemed the therapy of choice according to local standard of care with at least 1 of the following criteria fulfilled: a. Ta LG/G1, b. Ta LG/G2, and >=1 of the following risk factors: i) Multiple Ta LG tumors, ii) Solitary LG tumor >=3 cm

Have a susceptible fibroblast growth factor receptor (FGFR) mutation or fusion either by urine testing or tumor tissue testing (from TURBT tissue), as determined by central or local testing

Participants must be willing to undergo all study procedures (e.g., multiple cystoscopies from Screening through the end of study and TURBT for assessment of recurrence/progression) and receive the assigned treatment, including intravesical chemotherapy if randomized into that arm.