0. Mount iso-file R2021a_Windows.iso to virtual disk.
     For Windows 8 and lower you probably need soft like Daemon Tools Lite (or similar)
1. Run setup.exe from that virtual disk and if you see login/password/signin form (you gave access to internet for installer)
     then in apper left corner in "Advanced Options" select setup mode "I have a File Installation Key"
     If internet access is absent then required setup mode will be autoselected and you do not need to set setup mode
2. When you will be asked to "Enter File Installation Key" enter
     09806-07443-53955-64350-21751-41297
3. When you will be asked to "Select License File" select license.lic
4. Then select folder where you want Matlab to be installed. When you will be asked to "Select products" deselect component
     "Matlab Parallel Server" and select components you need.
     If you will leave all components selected matlab will need 32Gb of disk space and longer startup time.
     If you left only "MATLAB" - 3Gb of disk space
     You better setup matlab on SSD disk for better startup time, so most likely you do not want to waste SSD-disk size for nothing.
5. Then in "Select Options" select "Add shortcut to desktop"
6. Components setup progress may be shown incorrectly (for example allways show 0%) ... just wait.
     Or if installation process takes too long start to monitor growth size of folder where you are installing matlab
     If it size is not growing several minutes then restart setup
7. After installation is done copy file "libmwlmgrimpl.dll" to already existing folder
     "<matlabfolder>\bin\win64\matlab_startup_plugins\lmgrimpl"
     with overwriting of existing file (<matlabfolder> - is where you have installed Matlab)
8. Copy "license.lic" file to <matlabfolder>\licenses folder
     Alternatively you can just start Matlab. In that case you will got window asking you to select license
       First select "Activate manually without the Internet" and
       then in field "Enter the full path to your license file, including the file name" select "license.lic" file
9. Work with matlab :)
     If setup hang in step 1-6 then force to close setup and start again from step 1

P.S.
license.lic additionally to possibilities of license_standalone.lic gives Matlab permission to work from remote desktop (RDP)
  This allow not to use license_server.lic in certain cases

P.S.2
File Installation Key you give to installer actually depend on Matlab edition and type of license you want
  For standalone license use license.lic or license_standalone.lic and keys:
    For workstation use case (typical configuration)  : 09806-07443-53955-64350-21751-41297
    For cluster node "Matlab Production Server"       : 40236-45817-26714-51426-39281
  For floating license use license_server.lic and keys:
    For workstation use case (typical configuration)  : 31095-30030-55416-47440-21946-54205
    For cluster node "Matlab Production Server"       : 57726-51709-20682-42954-31195
