As for bitcoins lost forever, I think they're a gift to all hodlers.

I also find it difficult to estimate this.

One of the most well-known estimates was made by the blockchain analysis firm Chainalysis. In 2022, Chainalysis estimated that about 20% of all bitcoins ever created, or about 3.7 million bitcoins, were lost forever. This estimate was based on an analysis of bitcoin transactions that had not been moved in over five years.

Another estimate was made by the blockchain analysis firm Glassnode. In 2023, Glassnode estimated that about 21% of all bitcoins ever created, or about 4 million bitcoins, were lost forever. This estimate was based on an analysis of bitcoin transactions that were sent to addresses that are no longer active.