The Upgrade Wizard throws an error when upgrading projects containing reporting-related JS/CSS/etc. report viewer files. For example:

Could not find file 'C:\Program Files (x86)\Progress\Telerik Reporting R3 2023\Html5\ReportViewer\js\telerikReportViewer.kendo-17.2.23.1010.min.js'.

The files in question are present in the expected directory but they no longer have the version number suffix in their names ('-17.2.23.1010' in the example above). Copying the files and adding the suffix to the copies resolves the issue.