Lose touch with reality implies you were once in touch with reality.

Out of touch with reality is silent on whether or not you were ever in touch with reality.

can I use either of them to describe people who are addicted to video games?

Probably not.

The fact that someone temporarily inhabits a fantasy world, while playing computer games, reading a book or watching a film doesn't really mean they've lost touch / are out of touch with reality.

The phrases imply something quite deep and fundamental, that simply doesn't apply for a few hours 'in game'.

However, if your assertion is that that in some cases someone is so obsessed with computer games that they simply no longer have any regard for the real world, then you could probably use it. But that would be an extreme case.

Lose touch with reality implies you were once in touch with reality.

Out of touch with reality is silent on whether or not you were ever in touch with reality.

can I use either of them to describe people who are addicted to video games?

Probably not.

Just because someone feels an overwhelming need to play computer games doesn’t mean they’ve lost touch with reality.

Also, addict is often used in a non-medical way (especially with respect to pop culture), so a video-game addict might just be someone who enjoys playing video games a lot, but doesn't meet the clinical definition of addiction.

However, if your assertion is that in some cases someone is so obsessed with computer games that they simply no longer have any regard for the real world, then you could probably use it. But that would be an extreme case.