Where the numbers come from
The 0.8 g/kg/day figure you hear quoted everywhere is the Recommended Daily Allowance — Health Canada / IOM’s estimate of the minimum needed to keep a sedentary adult out of negative nitrogen balance. It is not an optimum for an active person, an older adult worried about sarcopenia, or someone trying to keep muscle while in a calorie deficit.
The 2017 ISSN position stand (Jäger et al.) reviewed decades of nitrogen-balance and lean-mass studies and concluded that 1.4–2.0 g/kg/day is appropriate for most active people. Helms et al. (2014) reviewed lean-mass retention during deficits and recommended ~2.3–3.1 g/kg of fat-free mass — roughly equivalent to 2.2 g/kg of total body weight for most lifters.
What the result doesn’t tell you
This is a daily target, not a per-meal prescription. Older adults specifically benefit from ≥ 0.4 g/kg per meal to overcome the “anabolic resistance” that comes with age. People on dialysis, with eating-disorder histories, or on GLP-1 receptor agonists (semaglutide, tirzepatide) may need very different targets — see a registered Canadian dietitian, not a webpage.