Have you also got a legacy powershell script that loads SharePoint dlls and runs CSOM code directly? It’s quite easy to convert to PnP PowerShell. But if you run out of time and just need to execute the script, then I have a quick tip for you.
First of all, a CSOM script can be recognized by Add-Type commands (or Import-Module) plus the SharePoint dll paths.
Loading the dll the old way.