I buy minecraft for windows 10 and when I open it it won't let me log in

Have you tried removing your profile and adding it again?

Have you restarted your device and trying to log in after the installation of the game?

yes i already tried that

I'm using freshly installed Windows 10, I reset the store and restarted, but this didn't change anything. Then I installed the Minecraft launcher, I logged in with my Microsoft account and it provided me the options for three versions with following buttons:

Minecraft Java Edition / Play demo

Minecraft For Windows / Install

Minecraft Dungeons / Buy Now

When I installed the Windows version the "Install" button turned to "Play", but when I launch the game it asks me to "Sign in" and then to "Unlock Full Game" by buying Starter or Master Collection.

When I clicked to redeem it for Windows in the first place, it took me to the online store where I logged into my actual account that I wanted it on, it put the code in for me and said "You own this game." above it or something of the such.

It was supposed to permanently give me Minecraft: Windows 10 edition for free.

So based on all this information, will I just have to buy Minecraft from the store myself?

There are a couple things to check. The "Sign in" isn't for your Mojang account, which is likely what you used to claim your free copy from the site, but instead, that is referring to a Microsoft Account. So verify that you're using a proper Microsoft
Account by trying to
sign into your Microsoft Account page here.

The next thing to check would be in Settings > Gaming > Xbox Networking. Check that page, and let us know if there is anything that is not "Connected" or "Up and running", or other items that look out of place. That might be preventing you from logging
in, as well.

Let us know what you see and we can help troubleshoot further.