Assuming the relevant accounts are both connected to Ember, this is the category that should be used and more information on that can be found here.
Why can't I see the "Transfer between business accounts" category?
If you only have one business account connected to Ember you will not be able to see the "Transfer between business accounts" category any more. This is because if you have only one business account it should not be feasible to have a bank transfer. If you have transferred funds to a personal account this needs to be recorded as dividends/salary/director's loan depending on what was intended.
Please note that the "transfer between business accounts" category shouldn't be used if you're transferring money from a tax "pot". That should be assigned to "Prepayments" and you can read more on that here. If your pot accounts are not connected to Ember you can use "Prepayments" for transfers - or if you have multiple bank accounts you can continue to use "transfer between business accounts".