Buy GBTC or ETHE stock in the IRA account

[greentech2]

I see the stock of GBTC Grayscale Bitcoin Trust going up a lot.  I check its market cap in Yahoo Finance is $8.254 billion.  I see ETHE Grayscale Ethereum Trust in Yahoo Finance but its market cap is N/A.  I think the stock price of GBTC is premium higher than Bitcoin price.  I can not buy bitcoin in my IRA account so GBTC is the only choice.  GBTC Discount or Premium to NAV (Bitcoin) is 24.79%.  Can I buy GBTC when the Discount or Premium to Bitcoin is low like 20% then sell GBTC when the ratio goes high like 40%?  I think it is a good strategy to trade GBTC and Bitcoin to make profit.