If you are unhappy with the recent news around compatability behind Odyssey and Horizons in the Odyssey release (or any other reason), you are likely eligible for a full refund under steam/epic and forntiers own refund policy.
Elite Dangerous: Horizons players cannot share a gameplay session with those playing Odyssey. However, Odyssey owners will be able to share a session with and play with those in Horizons by launching the game in Horizons mode – though if they do this, they will temporarily not have access to the new Odyssey features.
Frontier Developments Pre-Order Refund Policy
For players who have made purchases directly through frontier:
You may cancel a pre-order for a Digital Product up to and including the day before the release date of the relevant Digital Product by contacting Customer Services clearly stating your order number and item(s) to be cancelled.
Find the purchase you would like to refund and click on it. If your purchase is not listed, it falls too far outside of our refund window and is ineligible for a refund. (This should not apply for Pre-Order Games)
Select the problem you are having with the product.
Next, click I'd like to request a refund.
Fill out and submit the request form.
You should receive a confirmation email that your request was successfully submitted.
Epic Games Pre-Order Refund
For players who have purchased Odyssey through the Epic Store:
You can cancel your pre-purchase and get a refund at any time before release. After the game is released, you can request a refund within 14 days if you have not played the game for more than 2 hours. For purposes of this policy, “release” includes any playable version of the game, including early access, beta, and alpha versions.