Nintendo Switch 2 game cards has been one of the most controversial topics: Nintendo said that some games (at least its own first party games) will come with Game-key cards, which don't contain the full game data, but rather work as a "key" to download the full game online. This caused discomfort for many players, as it makes Internet obligatory (at least for the first time to download the game), distorting the value of physical games.
However, in reality this isn't much different to how PlayStation Blu-rays have been working for a while. And in case there was any doubt, the game card is mandatory every time you want to play the game, and they are not tied to your Nintendo Account in any way. This means that second-hand market will work as always: you can buy and sell used games without any worries, or lend them to friends and family.
Nintendo confirmed that to GameSpot. It may sound obvious, but in a world where a Mario Kart game will become the most expensive game of the generation, it's good to search for complete certainties...
That said, it appears that some publishers will sell their full games on the game card, as it happens with most Switch games. That will be the case for Cyberpunk 2077 Ultimate Edition, coming on a 64 GB game card.