How to enable this back?  

If you hack something, at least keep notes.

If you plan to make a change to the registry, export the key(s) you are going to change and keep them aside.

As to the change, it's going to be something equivalent to a group policy.
E.g.


or perhaps
Enable or Disable Changing Start Layout in Windows 10

Note that your symptom is the subject of a post following that tutorial- and in detail in posts following:
Add or Remove Folders on Start List in Windows 10

Try this:
https://answers.microsoft.com/en-us/...-528f7e730e591. Open command prompt with admin permission2.Execute these commands then restart the computerreg delete "HKCU\Software\Microsoft\Windows\CurrentVersion\Policies" /freg delete "HKCU\Software\Microsoft\WindowsSelfHost" /freg delete "HKCU\Software\Policies" /freg delete "HKLM\Software\Microsoft\Policies" /freg delete "HKLM\Software\Microsoft\Windows\CurrentVersion\Policies" /freg delete "HKLM\Software\Microsoft\Windows\CurrentVersion\WindowsStore\WindowsUpdate" /freg delete "HKLM\Software\Microsoft\WindowsSelfHost" /freg delete "HKLM\Software\Policies" /freg delete "HKLM\Software\WOW6432Node\Microsoft\Policies" /freg delete "HKLM\Software\WOW6432Node\Microsoft\Windows\CurrentVersion\Policies" /freg delete "HKLM\Software\WOW6432Node\Microsoft\Windows\CurrentVersion\WindowsStore\WindowsUpdate" /f

If you are willing to do a lot of investigation then you will probably find a way to undo the tweaks.

Create a new user then toggle the relevant settings whilst monitoring the Registry with
NirSoft RegFromApp
or
RegShot - there's some guidance at How to Use Regshot To Monitor Your Registry - HTG

Then you'll know where to look in your current user's Registry.

Denis

Obviously you know this isn't the way to do things

that's after making customization! so not possible

'
You're lucky you found the regedit!!