Red dead 2 for xbox is already purchased, can i get it for free on pc?

the title does not have the play anywhere feature - you will need to purchase it again

no, as they are 2 different versions and RDR 2 is not a play anywhere title.

I already own red dead redemption 2 on my Microsoft account for Xbox so why can't I use my Microsoft account to install the game on my PC?

Because like many other games, Red Red Redemption 2 isnt a play anywhere title meaning if you bought it for Xbox then that only entitles you to the Xbox version of the game.

If you want to play the PC version then youll need to purchase the PC version.

Firstly, the retail full version of Red Dead Redemption 2 on disc already includes Red Dead Online so unless you have transitioned to a digital only console, you wouldn't need to purchase it again.
Secondly, which digital version did you purchase? There is the full game Red Dead Redemption 2. There is also Red Dead Online, which is obviously the online part. And then there is Red Dead Redemption 2: Story Mode, which is just a DLC for Red Dead Online (owning Red Dead Online is required) which allows you to play the single player campaign.
Please check your purchase history to see which one you have purchased.

So if i purchase red dead online,will i immediatly be able to play story mode,i wont need xbox live so that i can play red dead 2 story mode will I?

I purchased red dead 2 story mode but i cant seem to install it, so all i need is internet connection and to purchase online mode and it will immediatly work?