ポートをリッスンしているプロセスが何をしているか調べる

 PS> Get-NetTCPConnection -LocalPort 3000 | select OwningProcess
 
 OwningProcess
 -------------
         12345
 
 PS> Get-Process -Id 12345
 
 NPM(K)    PM(M)      WS(M)     CPU(s)      Id  SI ProcessName
 ------    -----      -----     ------      --  -- -----------
     61    26.25      39.82       0.39   12345   1 node

PowerShellを管理者権限で起動する

 PS> handle64.exe -p 12345
 
 Nthandle v4.22 - Handle viewer
 Copyright (C) 1997-2019 Mark Russinovich
 Sysinternals - www.sysinternals.com
 
    44: File  (RW-)   C:\sources\my-app
   238: Section       \Sessions\1\BaseNamedObjects\node-debug-handler-31652
   268: File  (RWD)   C:\sources\my-app\node_modules\webpack
   27C: File  (RWD)   C:\sources\my-app
   280: File  (RWD)   C:\sources\my-app\node_modules\webpack-dev-server\client\clients
   284: File  (RWD)   C:\sources\my-app\node_modules\@pmmmwh\react-refresh-webpack-plugin
   290: File  (RWD)   C:\sources\my-app\node_modules\webpack-dev-server\client
   298: File  (RWD)   C:\sources\my-app\public
   29C: File  (RWD)   C:\sources\my-app\public
   2C0: File  (RWD)   C:\sources\my-app\node_modules\webpack-dev-server

• handle64.exeはSysinternalsのコマンド

参考

https://docs.microsoft.com/en-us/sysinternals/downloads/handle