This is correct, gains in ISAs are tax free and have no impact on cgt allowance. So if cryptocurrencies were a good investment an ISA would be an excellent place to hold them and convert gains to currency you can spend, but I don’t think any isa providers support them.
Which is a particularly useful case for Bitcoin ETFs
They don’t have impact unless you sell or cash out.
The same goes for many other assets you pay cgt only when the profit is realized.
No, you don’t ever pay cgt on gains in an isa, that’s the whole point of them. So if you could hold bitcoin (at the moment only an etf is possible), there are no taxes on gains.