Recording a VST and an external synth together

Hi,

I very much like to combine my external synths/keyboards with various VSTs and prefer to have the VST be recorded as MIDI only and the external synth as audio only. I remember being able to do this relatively easily in the older versions of FL Studio (although I do not remember if I honestly did anything differently). However, either the behavior in the new version of FL Studio (20.8.3) has changed, or it's because of the different audio interface I use (Zoom R8), but what happens now is that, when I assign the Pigments 3 VST from the channel mixer to a mixer track and set the input channel in the mixer track to my audio interface's stereo input, both the VST and the external synth get recorded into the same wave file. I don't want this and want the external synth only in the wave file, but I have no idea what the correct/proper way is to actually do this. I remember with the old versions, FL Studio would just somehow sort it out by itself, but now, the behavior seems different, and I don't have any idea how to record the VST and the external synth at the same time, where the VST just gets stored as MIDI data and the external synth only gets recorded as audio. Can anyone help?