Gemcitabine/Cisplatin Plus Cemiplimab With or Without Fianlimab in Localized Muscle-invasive Bladder Cancer (NeoSTOP-IT)

The goal of this clinical trial is to learn if gemcitabine/cisplatin plus cemiplimab with or without fianlimab works to treat bladder cancer in adults. The main question it aims to answer is: Can gemcitabine, cisplatin, and cemiplimab with or without fianlimab treat bladder cancer? Participants will be randomly selected (like the loss of a coin) to treatment with gemcitabine, cisplatin, cemiplimab, and fianlimab or gemcitabine, cisplatin, and cemiplimab. Participants will: * Undergo transurethral resection of bladder tumor (TURBT) followed by the start of treatment, receive 4 cycles of treatment (21 day cycles) * After 4 cycles of treatment, patients will undergo repeat maximal TURBT with imaging * Participants with a complete response will continue maintenance cemiplimab or cemiplimab/fianlimab for 13 more cycles with imaging every 3 months * Participants without a complete clinical response will undergo cystectomy (bladder surgery).