Hi dear friend, first of all, I hope that everything is very well with you and all yours, that peace and light are always in your paths.
I had the same problem as you when I do a clean install, the "Windows Security" icon had a red cross and when I tried to open it it only indicated that I had to download the app from the store, but since Microsoft doesn't do anything well, the store doesn't show no app or solution for this so I looked in all the questions answered by "Microsoft consultants and also Independents" who usually respond with vague instructions, not to say without any sense, or even "solutions" that besides not solving anything, still indicate reinstall the system when they have no alternative, because they don't know how to solve it, it seems that none of them has the embarrassment to solve such questions and Microsoft doesn't seem to care about any of that.
There are definitely three ways you can solve this without having to reinstall Windows 11, and they are easier than any other fancy method full of steps that don't result in anything...
First option... The first is to do a search in the Windows directory for Microsoft.SecHealthUI_8wekyb3d8bbwe.appx if you find it there, all you have to do is click on it and select install and that's it, problem solved.
If you need, you can use a smaller softwares called Everything to do the search, it literally finds anything inside your HDDs and it is very practical, safe, can be used with a dark interface and also super fast . Just search it on GitHub and download it's totally free app.
Second option... You can connect another HDD from another machine where you have Windows 11 installed and use the same method described above, looking for that file in the Windows directory of this other HDD and installing appx in the same way...
Third option... You can download it directly from the link below, it will show the file name as 36075e35-e566-4f57-8696-6a97aee50956, change this name to Microsoft.SecHealthUI_8wekyb3d8bbwe.appx and after downloading install it in the same way just double clicking on the same and that's it, problem solved without any solution full of steps that only lead to the abyss of ignorance...
Follow the direct download link from Microsoft servers, remember to rename it, otherwise it will not be able to install.
Microsoft.SecHealthUI_8wekyb3d8bbwe.appx
If you were able to solve your problem using my directions, please mark it as an answer.
A big hug and may the Light always be upon you!
