If you are running on Windows 11, you will have an option to use Mica window backgrounds (the default)
or to switch to Acrylic.
Acrylic was introduced as a semi-translucent frosted glass appearance. It is used extensively in Windows 10, and on Windows 10 Acrylic will be the only option available.
Beginning with Windows 11, a new window background style, Mica, was introduced. Mica is much more subtle. It is not transparent, but dynamically changes based on your window's position and your desktop background picture. It is the preferred visual style when running on Windows 11.