If you're running into issues early on it helps to activate debugging. Do this if the page loads as a white page and you only get a generic error message. There are two important ways to do this:

Send more Error Information to the Client

In the appsettings.json you can set a few toggles which will tell Blazor to include more information about issues. To see what these settings are, open the console in the browser (F12) and follow the instructions there. 

Activate extensive Error Logs on the server

Open the web.config and change the stdoutLogEnabled="true" like this:

<?xml version="1.0" encoding="utf-8"?>
 <location path="." inheritInChildApplications="false">
       <add name="aspNetCore" path="*" verb="*" modules="AspNetCoreModuleV2" resourceType="Unspecified" />
     <aspNetCore processPath="dotnet" arguments=".\Oqtane.Server.dll" stdoutLogEnabled="true" stdoutLogFile=".\logs\stdout" hostingModel="inprocess" />

You can now find detailed logs in the logs/stdout folder beneath the web folder. 

Difference for Oqtane source version

While default web.config file is usualy ok for Oqtane install version, to enable logging in Oqtane source version (vs2019 and iisexpress) aspNetCore arguments attribute needs to be adjusted because Oqtane.Server.dll is on different path .\bin\Debug\net5.0\Oqtane.Server.dll like here web.config.

<aspNetCore processPath="dotnet" arguments=".\bin\Debug\net5.0\Oqtane.Server.dll" stdoutLogEnabled="true" stdoutLogFile=".\logs\stdout" hostingModel="inprocess" />