Convert disc to digital game

The only way to get your disc game working on the "All digital" edition of the Xbox One is to purchase the game digitally.

It's not possible to "convert" a disc game to a digital game. Otherwise you could buy a disc, convert it to digital, and sell the disc to someone else who would then convert to digital, sell the disc and so on, until the whole world has the game digitally,
and only one disc was sold.

So the only way to get a digital copy of your disc based game would be to buy the game digitally again.

Short answer: No.

The reason is, that otherwise people would buy a physical disc, convert it to digital at no cost, and then sell the disc to someone else, who would then convert the disc to digital at no cost, and sell the disc again.

This can go on until the whole world owns the game, while the game maker only has sold one disc copy of the game, which would mean a huge financial loss for the game maker.

So no, because of that, you can't convert a disc game to a digital game "without extra cost".

As stated in these post, you cannot convert your disc games to digital and the advertisement for playing existing games possibly had some fine print stating it was existing "digital" games you own. Converting the disc games to digital would be nice but
the developer would have to sign off on it and it is not just a Microsoft decision.

It plays your existing digital games. There is currently not a way to convert disc games to digitial

The only way to convert it would be to purchase the game digitally. There is no discount for owning the disc