Search the event log for sql server restarts with this powershell query

get-Eventlog application | where-Object { $_.source -like "MSSQL*" -and $_.Message -like "SQL Server is starting*" }

With alias

Or more briefly:

get-Eventlog application | ? { $_.source -like "MSSQL*" -and $_.Message -like "SQL Server is starting*" }

Specific date range

Or for particular message / date range

get-Eventlog application | where-Object {
				$_.Source -like "MSSQL*"
	-and	$_.TimeGenerated -gt ([datetime]::parseexact("2021-07-01", "yyyy-MM-dd", $null))
	-and 	$_.TimeGenerated -lt ([dateTime]::parseexact("2021-07-13", "yyyy-MM-dd", $null))
	# -and $_.Message -like "SQL Server is starting*"
	} |
		select -prop timegenerated, message