Bandai Namco has never released a fully featured, officially licensed online Tamagotchi game that replicates the handheld experience in a browser or app. The brand treats digital pets as physical devices (Tamagotchi Connection, Tamagotchi On, Tamagotchi Pix, Tamagotchi Uni) with optional app companionship—not standalone online games.
Want the real thing? Buy a Tamagotchi Uni (2023) — color screen, Wi-Fi, Tama Arena, downloadable content, app sync. It is the online Tamagotchi—just with a required dongle.