Can I buy VBucks from Microsoft Store and get it to Fortnite PC?

you purchased vbucks via epic on pc, then you need to load fortnite on pc to add them, to get vbucks on xbox you have to purchase via microsoft store or in game on xbox

https://www.epicgames.com/fortnite/en-US/faq

Epic Games stated : "

Q: Do I still have access to all my items and progress on all other platforms?

A: Yes. As long as you’ve linked your account to your Epic Games account, all purchased content is present and all progress is recorded across
all supported platforms."

Yes, that is correct. Items and progress but not purchased Vbucks.

No you can't.

After you buy the vbucks on ms store, you need to login to the game on xbox to add the vbucks to your account.

Since you don't have an Xbox , this isn't possible for you.

I’m pretty sure anything related to Microsoft and your account, takes lead to your Game add-ons

You should told Epic games to allow this