The Spurs are doing something no team has done since 2018 (airalamo.com)
This article about the team speed of the Spurs gives statistical information that reinforces my view that the problem with the Spurs in the second half of games--and especially in the 4h quarter--is the direct result of running out of gas due to the pace they play at in the first half. Their team speed works in the first half of games as they harass the other team into miscues, turnovers, steals and generally bad shooting as the clock runs down. On offense they get break-away fast breaks and are able to slice up the other team's defemse before they get set.
It's team basketball at its best, but it has its limitations. The amount of energy expended in the first half drains the players and they simply can't duplicate the effort in the second half. They wind up with no legs under them and can't defend as well. Similarly, with the spring out of their legs, the shots start falling a little short on jumpers and they can't get to the basket on drives as easily.
The team is well-conditioned, but I contend that none of the players should be playing over 30 minutes if maximizing the team's speed is the game tactic of choice. I personally think it is the right way to go since we have no super-stars, but instead have a number of fast players with a second level of skill sets. You can see the impact of 38 minutes a game on Murray in the 4th quarter when his shots aren't falling. Same with White and Keldon.
The answer is to cut their minutes to give them meaningful breathers. Give some of the other players like Jones and Diop extended minutes with orders to run like to keep the pressure on while the others catch their breath and refuel energy.