Available for transfer?
The amount available for transfer is the cash amount that you can transfer to your fixed contra account (= the current account at your bank that you linked to your Bolero account).
Exchanges settle trades two trading days after the trade date, which is the value date of the transfer. It is possible to already register an outgoing transfer before the value date, but it will not be executed until the value date.
The amount can already be used for new purchases before its value date; these purchases will also only be settled two trading days later.