Hi, let me help you.
Please try restarting Windows Explorer itself: press Ctrl+Shift+Esc to open Task Manager, find "Windows Explorer" in the list, right-click it, and choose Restart. That alone fixes it a surprising amount of the time.
If that doesn't bring the Start button back, try a straightforward reboot next, since a partial driver or shell load after the repair could be the culprit. Should that still not work, open Task Manager again, click File, then Run new task, type powershell, and run it as administrator. In that window, paste this command and hit Enter: Get-AppXPackage -AllUsers -Name Microsoft.Windows.ShellExperienceHost | Foreach {Add-AppxPackage -DisableDevelopmentMode -Register "$($_.InstallLocation)\AppXManifest.xml"} That re-registers the shell component responsible for the Start button and taskbar, and it's usually the fix when a repair or reinstall leaves that part broken.