The fix is divided in two parts, as a prerequisite disable SIP for now:
1. Fix the installer
A. Download pacifist https://www.charlessoft.com/cgi-bin/pacifist_download.cgi?vers=3.6.2&type=zip install it and after mounting the matlab_R2021a_maci64.dmg go inside the icon InstallForMacOSX.app -> Show package contents -> Contents -> MacOS, open InstallForMacOSX with Pacifist;
B. Drag the InstallForMacOSX root folder to your desktop and rename it to InstallForMacOSX