It's speculated that the patent in question (or one of) is one that essentially protects the gameplay loop of Pokémon Legends Arceus.

https://ipforce.jp/patent-jp-P_B1-7545191

Running the first claim of the invention through Google Translate yields this massive run-on sentence description:

The computer causes a player character in a virtual space to take a stance to release a capture item when a first category group including a plurality of types of capture items for capturing a field character placed on a field in a virtual space is selected based on an operation input of pressing an operation button, and causes a player character in the virtual space to take a stance to release the capture item when a second category group including a plurality of types of combat characters that engage in combat is selected, and determines an aiming direction in the virtual space based on a directional input, and further selects the capture item included in the first category group when the first category group is selected, and the combat character included in the second category group when the second category group is selected, based on an operation input using an operation button different from the operation button , and causes the player character in the virtual space to take a stance to release the capture item when a first category group including a plurality of types of capture items for capturing a field character placed on a field in a virtual space is selected, and determines an aiming direction in the virtual space based on an operation input using an operation button different from the operation button, A game program which, based on an operation input of releasing the operation button pressed when having the player character perform an action, has the player character perform an action of releasing the selected capture item in the aiming direction if the capture item is selected, and has the player character perform an action of releasing the selected combat character in the aiming direction if the combat character is selected, and when the capture item is released and hits the field character, makes a capture success determination as to whether the capture is successful, and when the capture success determination is judged to be positive, sets the field character hit by the capture item to a state where it is owned by the player, and when the combat character is released to a location where it can fight with the field character, starts a fight on the field between the combat character and the field character.

Essentially, Nintendo has a patent on video games that involve throwing a capsule device at characters in a virtual space to capture them and initiate battle with them. In other words, they have a patent on the concept of Poké Balls (as they appear and function in Legends Arceus, specifically).

Palworld has "Pal Spheres", which are basically just Poké Balls with barely legally distinct naming.

If this sounds like an unfairly broad thing for Nintendo to have a patent on, I'm not so sure I agree. It's not like they're trying to enforce a blanket patent on all creature collectors. Just the concept of characters physically throwing capsule devices at creatures.

If you think about it, that's kind of the one thing that sets Pokémon apart from others in the genre. If there's anything to be protected, that's it. It's literally what Pokémon is named after--you put the monster in your pocket, using the capsule you threw at it.

Palworld could have easily dodged this bullet. They claim they aren't inspired by Pokémon, and that they're instead inspired by Ark: Survival Evolved. Funny, then, that Ark doesn't have throwable capsules, yet Palworld decided to add them. I'm not sure I buy their statement. And if this is indeed the patent being violated, I don't think a court will buy it either.

I'm not trying to be a Pokémon apologist here. I want Palworld to succeed and give Pokémon a run for its money. But looking at the evidence, it's clear to me Pocketpair flew a little too close to the sun here. And they're kind of idiots for it.

I'm just surprised they aren't getting nailed for the alleged blatant asset theft.