To Install PowerShell 7 using winget, first find the Id.
PowerShell
winget search Microsoft.PowerShell
Name Id Version Source
---------------------------------------------------------------
PowerShell Microsoft.PowerShell 7.3.6.0 winget
PowerShell Preview Microsoft.PowerShell.Preview 7.4.0.5 winget
Then install it using the noted Id.
winget install --id Microsoft.Powershell --source winget