How can I update macOS for App downloads on my MacBook

How far you can update macOS will depend on which particular Mac you have.

For instance, you can update a MacBook (Retina, 12-inch, Early 2015) as far as macOS 11 (Big Sur), but no further. A MacBook (Retina, 12-inch, Early 2016) can run macOS 12 (Monterey).

What does it say about your Mac model and hardware release year in the About This Mac dialog in the Apple () menu? (Include the screen size, the "Air" or "Pro" if applicable, and the time of year if applicable. Don't post your serial number.)

It may turn out that your machine is eligible for a macOS update.

If it says you need a newer macOS version then you need a newer macOS version.

Not every application is built for or supported on earlier software versions.