Only a very tiny portion of bitcoin
Is properly "green". There are some oil wells in the US that are not near any natural gas pipelines so the excess natural gas that comes from the well was simply flared off. Some bitcoin miners set up operations there to use that gas that would otherwise be uselessly burned. So you can argue that's green, since it isn't increasing emissions at all (it may actually slightly reduce them, as they would have incentive to reduce leaks they would have previously ignored)
There are also a lot of very much not green practices - just saw an article that in Pennsylvania bitcoin miners have been opening up old gas wells that were capped a few years back when the price got too low and bringing in natural gas generators. So they're creating new emissions but trying to claim they are like the operations using flare gas - when there is a perfectly good pipeline that could bring that gas to market where it would provide useful economic work instead of the total waste that is bitcoin.
Simply using green energy to mine bitcoin is not green in any way, because that's forcing other energy users who would have used it to use fossil fuels instead, so even if you set up in next to a dam every megawatt of power you use is a megawatt that someone else has to replace with fossil fuels.