It’s healthy to do heavy squats, but can it become unhealthy if it gets too heavy?
As an example, we can take a man who weighs 80 kg.
It is healthy for him to squat 1.5 x bodyweight (120 kg) 5 reps RIR 4-2.
But is it healthy for him to squat 2 x bodyweight (160 kg) 5 reps RIR 4-2?
Strength is muscular force production measured in a specific context, e.g. a task or test. Generally speaking, stronger is better for sport and health until the pursuit requires use of harmful substances or behaviors (e.g. avoiding conditioning, social interaction, etc.).
We don’t know how strong is “strong enough” for optimal health trajectory, but it’s probably stronger than what most people think if they don’t lift. And it’s probably not quite as strong as what serious lifters would imagine. The line of diminishing return for health probably happens sometime around ~ 1.5x BW squat for men and 1.25x for women, though that’s mostly speculation.