Cryptocurrencies are not really suitable (at this time) for large scale purchases.
There are several reasons, the first being that if one wants to skirt sanctions, the fact that all transactions are recorded on the blockchain makes them transparent to those willing to make the effort to track them.
More generally, if one is talking of millions of dollars in a single transaction, the liquidity is not there to enable easy transactions. That will almost certainly change in the future and is, of course, not an issue for most people or businesses.
Crypto is great for individuals making relatively low-value transactions in terms of security and speed and is being used in, for example, Ukraine, by both the government and individuals. If I were a refugee, for example, I would store as much of my wealth as possible with the keys stored in a form that did not even need me to carry them on my person.
[EDIT]
This story on Zerohedge carries some info about the possible use of crypto.
I had not realised that Putin himself had noted that liquidity was seen as an issue for using crypto. However, at least one spokesperson seems to suggest crypto as a possibility - among other options.
If true and it did come to pass, then the very fact of Russian acceptance of such payments would tend to increase market liquidity. Given that the spokesperson made it clear that such transactions would only be available to 'friendly' parties, the secrecy issues might not be such an issue.
https://www.zerohedge.com/markets/russia-open-selling-natural-gas-bitcoin-gold