If you are installing anything below SQL 2014 then the SQLAgent account is the first account that gets validated. If it comes up with an error this may mean the account is invalid, but it can also mean you have a problem contacting your domain controller.
If you verify that the account and password are OK, then you need to direct your troubleshooting around comms issues between the serve and the domain controller.
Dave has identified one possible problem and its solution. Even two years ago (2014) you did not need to put the fdqn into the adapter settings to get the comms to the domain controller working, but today it seems that it is necessary.
Original author: https://github.com/SQL-FineBuild/Common/wiki/ 1-click install and best practice configuration of SQL Server 2019, 2017 2016, 2014, 2012, 2008 R2, 2008 and 2005.
When I give food to the poor they call me a saint. When I ask why they are poor they call me a communist - Archbishop Hélder Câmara