There are no taxes incurred on the gains or losses realized inside a traditional or Roth IRA when trades are executed. With a Roth IRA, the dollars come out tax free within certain constraints (age or account lifetime, roughly speaking), with contributions sourced from after tax earned income. With a traditional IRA, taxes are due when withdrawn. They can only be funded with dollars, not shares or assets. You can direct your investments with a self directed IRA for esoteric asset classes, but the IRS has strong guidelines around this to prevent self dealing as well as requiring transactions to be “arms length”. You cannot borrow against these accounts (although you can roll traditional IRA funds into a 401k and borrow against it there as a fixed term loan at an interest rate set by the plan administrator that follows the benchmark rate).
The loophole Thiel used no longer exists.
https://www.propublica.org/article/lord-of-the-roths-how-tec...