If you are using a high-resolution monitor (like a 4K screen), your computer uses "Scaling" to make text and apps readable. If you have a 4K screen and leave scaling at 100%, text would be microscopic. Windows often sets this to 150% or 200% automatically.
Sometimes, a Windows Update can mess with these scaling settings. If the system suddenly switches from 150% scaling to 300% scaling, or if you plug in a second monitor with different scaling preferences, your icons may balloon in size unexpectedly. This is the computer trying to help you see, but ultimately just cluttering your workspace. why are all the icons on my desktop big