The error number 0x80073701 (ERROR_SXS_ASSEMBLY_MISSING) and inability to pin deployment during IIS installation on Windows Server 2019 suggest that there may be a problem with a particular update (KB4561608) necessary for the installation. You might attempt the following troubleshooting steps:
- Check for pending updates:
- Manually download and install the problematic update:
- Clear Windows Update cache:
- Use DISM and SFC tools:
It is advised to contact Microsoft Support or the Windows Server community forums for more help if the measures above don't address the problem. They can offer precise advice and problem-solving techniques adapted to your circumstances.