About the pollution of gold vs bitcoin : Bitcoin consumes more energy that gold for mining a given value :

See :

https://digiconomist.net/bitcoin-mining-more-polluting-than-gold-mining

And :

https://www.nature.com/articles/d41586-018-07283-3

Also, the hardware required to mine bitcoin evolve very rapidly and is obsolete every 1.5 year on average.

Currently it's estimated that 12 000 tons of hardware are produced and wasted each year (they cannot be used for anything useful after that)

https://digiconomist.net/bitcoin-electronic-waste-monitor/

Hardware is mostly done of metals (aluminium, copper, iron, ...).

So that's basically more than 10 000 tons of metals mined each year : 3 times the weight of gold extracted on the samed period, with comparable concerns about pollution of soils than mining gold.

Mining bitcoin is basically physical mining, with all the pollution associated to it + a tremendous usage of energy (requiring, itself, either high carbon footprint , or high usage of metals, for renewables).

Bitcoin is ot physically sustainable. We cannot accept this at the time of climate change and 6th mass extinction, both threatetning life and human cizilization in the medium term (50/100 years)