What exactly are you trying to achieve? Are you trying to send a "fixed" amount with a "fixed" fee?
Anyway, you have specified 0.00026433 BTC per kb... your transaction is 0.258 kb as noted in the confirmation dialog.
0.00026433 BTC/kb * 0.258 kb = 0.00006819 BTC which is exactly what the app said it was going to add.
Not quite sure where you got "0.00001759302 BTC" from? I don't see that value shown anywhere in your post?
Looking at your screenshot, it seems you have a total balance of 0.00128033 and you're trying to send out 0.00101600 and use the remainder (0.00026433 as the fee). Your best option is to go into "Settings" -> "Options" -> "Wallet" and then make sure that "Enable coin control features" is checked. (You may need to restart the app)
Once that is switched on, when you go to send... click the "inputs" button...
then select all the inputs... and click OK. Then you should find that the "total at least" option becomes available which will let you specify a "fixed" fee.
WARNING: doing this is likely to result in a fee that is going to end up being very "low" compared to recommended fees. For example, for your transaction 26433 / 258 bytes = 102 sats/byte