I have heard that bitcoin is not supported in some countries. But why ? Is it because bitcoin is risky ? Some countries even declare 6 months jail if her people use bitcoin. Is it fair ? I mined few cryptos and have left mining. It was fun and challenging too. But I never got any clear answer. What does my gpu actually do ? I pay electric bill, my room temperature goes high and I get paid. With actually no skill on pc hardware and software. Whole thing is still pretty unclear to me
Bitcoin is "supported" anywhere there are computers. Bitcoin may be illegal or banned in various countries based on the laws in those jurisdictions.
As to why, the most likely answer is that the countries are not free and do not like the freedom that Bitcoin brings. The governments (and people running them) want to control people and keep them from being able to conduct commerce (and everything else) freely. Is that fair? Of course it isn't fair, but the people running the governments have the guns and are willing use them to suppress their people in order to keep power and enrich themselves. The solution is to avoid authoritarians/socialists/communists/fascists and have people who value freedom in charge of the governments. Look at China, devaluing the yuan daily which will impoverish (see, e.g. Venezuela) the people over time. All to retain their power and remain rich themselves.
Criminal activity can take place in any currency, but people use that as an excuse to retain their control.
As far as what the GPU (or bitcoin mining in general), take a look here:
https://en.bitcoin.it/wiki/Miningor
https://www.bitcoinmining.com