scrcpy is a tool made by Genymobile to mirror your Android Phone's screen(s) to your PC.
It's quite easy to use, only requiring you to enable ADB from your phone's developer options and running ./scrcpy
in a Terminal/Powershell window (that Terminal/Powershell should be opened in the folder you extracted scrcpy to)
There are many additional options available, like an ADB-Less mode which emulates a keyboard and mouse, or the option to use virtual displays (Developer Options)
Scrcpy can be downloaded here : https://github.com/Genymobile/scrcpy