I’ve recently really started to go in depth with flow motion because as you say, it’s quite random. Though to a point I’d have to disagree with its application but I’ll explain why because you pointed out something about serum which I can help with
So the reason why Flow motion is so random sometimes is because it’s based on a propper FM synthesiser. Fm synthesis is essentially a different way to modulate your wavetsble. The way you do that in FM synthesis is to take a second Oscillator and feed it into your first oscillator. Depending on the direction, wave type or other variable within the plugin this creates a new sound, as the wave shape has been altered. This is FM synthesis at its most basic. Then you ca. Ad LFOs and envelopes to alter the sound further, which will give you different sounds as you do so. That’s the most complex it gets… from this you can then affect you effects too. So flow motion imitates this almost perfectly within its sleek interface. It’s probably the best digital FM synth out there for that reason.
Now for Serum. Firstly, Serum is awesome, but it’s not a true Fm synth. It’s actually a PM synth that has a bit of FM capacity. The only part of FM synthesis you can do is the first part , affecting your first Oscillator with a second wavetable. To do this all you do is on your first oscillator in the FM part just click on the option for the other oscillator and turn it up. Essentially you’ll hear a bit of distortion and gain change but that’s pretty much it. This is basically just an imitation as Serum is trying to give you a flavour of FM synthesis. I’m real FM you’d also get phasingissues, clanging and possibly a bit of filtering because there’s so much going on… but Serum basically just thickens the part for you. You can then detune in Serum and it will still perform thr patch in PM as you’ll get that super thick synth sound, just with the extra thickness.
So Serum won’t do the same things that Flow Motion will do, but it does give a flavour. I hope that helps in terms of doing that in Serum, but I’d stick to learning Flow Motion to a level where you’d able to utilise that FM style to its most potential… and the great thing is you still won’t get exactly what you expect, but you’ll end up with more happy accidents… which is why I chose to talk about flow motion as my own too haha