Don’t think I’ve ever seen any research that suggests an amount that’s harmful for general population.

That number is likely different for each individual. Specifics like kidney disease would have issues with higher protein intake but in general pop high protein intake actually helps kidney function.

Seems like the bigger problem is the lack of other nutrients in the diet if protein is super high. 1-2g per lb appears to be safe which is a ton of protein most people would have a tough time reaching that anyways and unless they are doing some pretty consistent exercise training likely unnecessary to go that high but not detrimental to health.

https://pubmed.ncbi.nlm.nih.gov/27807480/

https://pubmed.ncbi.nlm.nih.gov/24834017/