Cryptocurrency can possibly be seen as a commodity, a form of digital gold (in the case cryptos like Ethereum, "digital oil"), stocks and shares in technology, and so on. But why would anyone want to use something as a currency that could potentially go up 2x, 10x, 20x in a few months?

Normal fiat currency like USD and EUR is relatively stable and lacks volatility, e.g. the price of a can of Coke hasn't changed much in 10 years.

Crypto is completely different. it's far more volatile and acts like stocks/shares or investments rather than national currencies

If I have holdings of fiat and holdings of shares - which should I use to buy a TV now? the fiat obviously

Why liquidize an investment that could be worth far more in the future over using fiat that will probably be worth approx the same?