Just upgraded to the latest linux AppImage from Electrum (I was several versions behind), and I see no "Transaction" tab in "Preferences".
"Transactions" tab no longer exists in "Preferences". That has been removed.
"Transactions" is the section where one can choose "replace by fee", so there seems to be no place to turn this off or on.
The option to enable and disable RBF has been removed since the version 4.4.0 of electrum and all transactions are automatically flagged as RBF.
There are several other settings under the "Transactions" tab also that don't seem to now be available.
Instead, there's a setting button in the window that pops up after clicking on "pay" button.
See the image below.