Since last month, I've gotten into trying out various Linux distros on my old laptop for fun, but no matter what, the WiFi will become unstable after a period of time. I've tried many different ways to solve it, with no avail. This issue persist throughout Linux Mint, Ubuntu Mate and KDE Neon. I can restart the computer or turn airplane mode on and off with F12 for a temporary fix, but the issue is really getting to me. Any solutions?

Are you sure it is not a hardware issue?

As a die-hard Arch user, I would refer you to the Arch Linux Wiki. I find it to be one of the most helpful and in-depth resources available.

https://wiki.archlinux.org/index.php/Network_configuration/Wireless

If you have access to the router, then change its settings. I suggest that you try changing the channel it is connected to. For example, if it is set of Auto, then connect it to lets say Channel 7. Also, change the encryption settings, from WPA to WPA2 (if not already done). I am guessing you are having this problem only with Linux and not on Windows (if you have multiple OS). If changing the settings did not help, then in all likelihood, the WIFI card of your system is having issues with the Linux operating system. I suggest that you buy an USB WIFI dongle, TP-Link or D-Link, any one of them is fine. These external dongles support a wide range of operating systems and will have latest updates available as well. Good luck.