After a long time of users asking, Valve has actually added an official Battery Charge Limit setting in the latest Steam Deck Beta update so you no longer need to use third-party tools.
Consider two decreasing lines, one with a slightly lower slope. Now imagine the steeper line starting higher on this graph, eventually the lines will cross and despite starting lower the shallower line will be higher.
Consider two decreasing lines, one with a slightly lower slope. Now imagine the steeper line starting higher on this graph, eventually the lines will cross and despite starting lower the shallower line will be higher.