Hey Peter, I have heard that theory put out but have yet to see any convincing data that would make me think a high-protein diet would be bad for bone health.
Whilst there are many issues that can contribute, I’d advise looking at vitamin D and vitamin K2 intake. Often people just think of throwing more calcium at the problem, when this will be largely ineffective if vitamin D and K2 are sub-optimal. If you think this may be an issue, I use a supplement by Da Vinci Labs of Vermont called ADK, which has those three fat-soluble vitamins in good doses.
That in combination with a high-protein diet and regular resistance training would seem like a prudent strategy to me for mitigating bone loss.
Hope this helps!