Just to note, you only get this error if you have chosen the "Preserve payment" option from the drop down box, since Electrum will not reduce the final output amounts in order to contribute more to the fee.
I just checked RBF strategies and there is no "Preserve payment" option.
The options are as follows.
- decrease change, or add new inputs, or decrease any outputs
- decrease change, or decrease any outputs
- decrease payment
Whatever strategy has been used by OP, it should allow decreasing the payment amount.
In the case of using the first option, the payment is decreased if there is no change and there is no extra UTXO.
In the case of using the second option, the payment is decreased if there is no change.
In the case of using the third option, the payment is decreased even if there's a change or there is extra UTXO.
Correct me if I am wrong, please.