The amount that you have not yet invested remains in your portfolio. This is your total Cash.
You can see this amount in your portfolio overview.
When you are actively investing, a part of your Cash will be reserved to pay for a possible closing Fee and/or Financing Fee. This is what we call a "Ring Fenced amount" (also see: What is the Ring Fenced Amount?). The rest of your Cash is available for trading or withdrawal.
When you close all your positions, your Ring Fenced amount will disappear and you can withdraw your total Cash.
If you have any further questions in regards to this, please feel free to contact us via email at BUX Support.