If you have a license, that will permit you to download R2021a (at this time.)
If you access from your Mac, then there will be a button to click to download the installer for MacOS. If you access from a different operating system, then click on the right-hand side of that button where the downward triangle is, and you will be permitted to select which operating system.
The installer for M1 is the same as the installer for Mac Intel: MATLAB uses "fat binaries" that include the binaries for both instruction sets.
