But, in BodePlot menu and in FFT meny there need be impedance selection and afaik there is and if user do not change default value is 50ohm. And this impedance setting mean EXTERNAL impedance (load) in scope input terminal. Impedance setting must be there and it is there. Other case it is impossible to select power scale for vertical (usually dBm). So, all places where need be 50ohm selection there is. (there is more, user can select also of course some other values just arbitrary or mostly used standard values like 75, 120, 300, 600 ohm etc)
In SDS1x04X-E models have never been internal 50ohm (but as @tautech told in scope input menu it have been in very old FW but without any effect as residue from other model).
And when user set these values in FFT or BP settings user is responsible about impedance matching in scope end of test setup, so if your transmission line is 50ohm need add external feed tthru terminator to scope input and select 50ohm in scope settings. In SDS1104X-E there is not this setting in normal xt scope setup menu. But there is also not power scale. This setting is with operating modes where user can also select power scale instead of voltage (or current). In this scope BP and FFT.