Today I tried installing the Developer version of SQL Server 2019 and I got the following error message during installation:

A previous installation required a reboot of the machine for changes to take effect. To proceed, restart your computer and then run Setup again.

I restarted my computer.  I re-ran the installation.  Same error.

I checked the setup log for more clues.  Here's where the setup log was located on my machine:

C:\Program Files\Microsoft SQL Server\150\Setup Bootstrap\Log\20210103_104409\Summary_mjw20_20210103_104409.txt

And here is an excerpt from the file:

Some quick Googling suggested that temporarily uninstalling the ODBC Driver might allow the SQL Server install to complete.

I went into the Apps & features application of Windows 10 and searched for ODBC.  Sure enough, I had previously installed Microsoft ODBC Driver 17 for SQL Server.  I clicked Uninstall and removed the driver from my computer:

I tried immediately re-running the SQL Server install, but it still failed.  

I rebooted once more.  This time the SQL Server install completed successfully:

SQL Server 2019 successfully installed
All three optional features I had selected Succeeded

Next, I went back into Apps & features to see if I would have to reinstall the ODBC Driver.  It looks like the SQL Server install handled that for me:

SQL Server 2019 installer (re-)installed the ODBC Driver 17 for SQL Server

Recap

When I tried to install SQL Server 2019, I received an error message about a pending reboot.  Here are the steps I followed to work around the error:

  1. Uninstall Microsoft ODBC Driver 17 for SQL Server
  2. Reboot the machine
  3. Install SQL Server 2019

Obviously, this will not be the fix for every instance of the "pending reboot" error, but it worked for me.  Your mileage may vary.