Samsung Galaxy S24+ will not connect to Wi-Fi or keeps disconnecting

The checks in more detail

If it is every network, the phone is more likely at fault. Turn on and off Airplane mode, restart, and check Settings, Connections, Wi-Fi, Advanced settings for Switch to mobile data, which moves to cellular when the Wi-Fi is weak and can look like a drop, and for Auto Wi-Fi settings that may disconnect from networks that seem poor. During tests, turn off Adaptive Wi-Fi and any VPN or private DNS that may be blocking traffic. In Developer or Advanced settings, a random MAC address is on for each network, which some routers dislike, so try using the phone MAC for that network.

Move closer to the router and check the signal: if it improves, the issue is range. A router set to Wi-Fi 7 only or to an unusual channel width may drop older phones, so try 5 GHz at 80 MHz and a standard security mode, WPA2 or WPA3. Update the phone and the router's firmware. Reset network settings in Settings, General management, Reset, Reset network settings, which clears saved networks and Bluetooth pairings, and test. Test in Safe mode, since a security or network app can interfere. If the phone fails on every network after all of that, Samsung service should look at the Wi-Fi hardware.

Check the phone's connection quality indicator by looking at the Wi-Fi details of the connected network: it shows the link speed and the band, and a link speed far below what the router should give points to distance or interference. If the S24+ shows 2.4 GHz at a speed in the tens of megabits while the router has a 5 GHz band, the phone may be stuck on the slower band, so forget the network and join the 5 GHz name directly if the router offers separate names.