Xiaomi
Turn Wi-Fi Auto Reconnect On or Off auf Xiaomi
MIUI remembers every Wi-Fi network your Xiaomi phone has ever joined and reconnects to it automatically once it comes back into range. This is controlled by a per-network setting called Connect automatically, not a global Wi-Fi switch.
Turning it off stops the phone from rejoining that one network on its own, while every other saved network keeps behaving as before. This is useful for guest networks, hotspots you only need occasionally, or a network with a weak signal that keeps interrupting your connection to a better one nearby.
Where to find the setting
Open Settings ➔ Wi-Fi, then tap the network you want to change and open the Menu. Toggle Connect automatically off or on, then tap Save to apply it.
If your phone struggles to reconnect to a network you actually want, check that this same toggle is switched on rather than looking for a fix in the mobile data or airplane mode settings. Those control different parts of the connection and will not change this specific behavior.