The team can put a clause in the contract that insures them against injury. In this case Dak is due $47.5 million in salary in 2024. If the Cowboys actually did purchase insurance against injury for Dak's salary, they can get paid a claim of $22.35 million (9 games salary) if Dak does not play again in 2024. The NFL treats the insurance payment as a reimbursement from the player and gives that amount of CAP relief to the team the following year. This means, IF Dallas bought a policy on Dak, AND he does not play again in 2024, they will get $22.35 million in CAP relief in 2025. Another reason to put Dak on IR and play out the season. Dak's CAP number next year is Just under $90 million. This will help that problem.
EDIT: There are potentially a number o clauses involved that will reduce the amount paid to the team. There are issues like deductibles, % or salary paid, games missed, etc.. It depends on what kind of policy the Cowboys took on Dak, and if they followed through and actually purchased a policy.