Accepted answer
Stated carefully, the mechanism is worth having straight, because it predicts which interventions can work and which cannot.
Absolute strength holds up better than scale weight during a deficit for a straightforward reason: strength is substantially neural and skill-based, and the contractile tissue you retain is being trained harder relative to its size. Grip strength and repetition maxima are therefore lagging indicators of muscle loss rather than leading ones, which is an argument for measuring both.
Protein target, worked: at 88 kg, a target of 1.6 g/kg is 88 × 1.6 = 141 g per day. Spread across three eating occasions that is roughly 47 g each, and the leucine threshold for a maximal muscle protein synthetic response is met at around 2.5 to 3 g of leucine, which corresponds to roughly 30 to 40 g of a high-quality protein. So three meals at 40 g plus one 25 g snack gets you to 145 g and clears the per-meal threshold each time. On 900 kcal that leaves about 340 kcal for everything else, which is the actual constraint.
The evidence for a higher protein intake preserving lean mass during an energy deficit is reasonably strong in resistance-trained populations and weaker in sedentary ones, with the meta-analytic estimates supporting intakes in the region of 1.6 g/kg over lower intakes when training is present[1].
One qualification: none of this is a clinical assessment, and unexplained loss of function rather than of mass is a reason to see someone rather than to adjust a programme.
The plateau is arithmetic. Treat it as arithmetic and the response follows.