Can I play on both xbox and pc with one purchase?

Short answer is:  At the same time with one account?  No.

It is much more about using separate accounts rather than how you get a license.  If you have an "EA" copy and your son has one through Game Pass, WITH separate accounts, you are good!

Hope that makes sense / helps!

From what I can tell, Battlefield 6 will likely not be on game pass. So I would like to know the answer to the OP's question with the caveat that it doesn't require 2 copies to be played at the same time.

I don't have an Xbox, but I have a buddy that has both an Xbox and a PC and it would be nice if he didn't have to purchase 2 copies if he wanted to switch over to his Xbox or something.

Historically, Battlefield games have always required you to pick your platform for this reason.  One copy per platform / account.  I am not arguing for or against, just relating what I know.

You might be right about Game Pass though as it is not explicitly mentioned here:

https://www.ea.com/games/battlefield/battlefield-6/faq

I am on xbox x with game pass ultimate, so i get pc gamepass, after the beta I downloaded bf2042 on my xbox console to complete the free bp, for me to play on pc i had to download the ea app and link my ea account to my xbox account in order to download and play bf2024, and I didn’t have to pay extra on the ea app because my xbox is linked to ea app.  I imagine it’s the same with all ea games and bf6, as of of today bf6 is not live only available on xbox and ea to pre order i pre ordered on xbox so i can post an update after release to see if i am able to download for bf6 for free on ea as i did for bf2042. Hope that helps

Also i will try and play bf2042 on pc and xbox at the same time on the same account 

2042 is on game pass which is why you can also download it for free on the ea app via pc game pass.

Bf6 will not be on game pass so will require a separate purchase for every platform you wish to play on.

If you managed to try it today, your feedback would be much appreciated. I have tried contacting EA support and the agent was giving me random replies instead of solving my query. The only BF that do not have shared licence was BFV, 2042 has this feature, even through EA Play copy. But I want to be sure BF 6 allows 2 Xbox with shared profiles and home console to play the game purchasing only 1 licence.

Thanks!

I play on both Xbox and PC, I purchased BF6 Phantom edition on Xbox, do I have to purchase the same version or can I just buy the base game for PC??

Thanks!