XAML code autocomplete (Intellisense) is disabled/ greyed out and can't be enabled

Hard case here:

After i installed a WinUI Preview version the WinUI Templates disappeared after weeks of installation (it's a known bug but i can't find the link anymore).
Nothing helped but a reinstallation with previous removal of all VS folders that i could found on my pc. (If i don't do it, the templates doesn't reappear after installation and there is also no XAML node in the Options dialog. I also removed everything by control panel/programs which has to do with development: Kits, Redistributables, SDK AddOn etc.)

Now i can't enable the mentioned options because it's greyed out.

I've tried all suggestions in the 2 links.

https://social.msdn.microsoft.com/Forums/vstudio/en-US/3db1698b-15ba-4396-b2ec-5e88cdb5f15a/xaml-code-autocomplete-intellisense-is-disabled-and-will-not-reenable?forum=visualstudiogeneral

https://stackoverflow.com/questions/17018978/visual-studio-intellisense-not-working-on-xaml-only-on-very-specific-circumstanc

Is this the right registry key as mentioned in the first link? (I've created all after 17.0 because there is no Text Editor key.)

“HKEY_CURRENT_USER\Software\Microsoft\VisualStudio\12.0\Text Editor\XAML”, Name: “Auto List Members”, Type: REG_DWORD. The default value is 1. Check if you have such value and it is 1.

I'm on VS 17.2.5 with Windows 11.

Solved:

https://stackoverflow.com/questions/61924136/intellisense-doesnt-work-in-large-xaml-file