question

There isn't a standard function for this in the Victron systems yet (hopefully it will be implemented in the feature), so we'll have to create a work around for now, like with using the 'ignore AC input' function.

I haven't tried it myself yet...but I think this should work to warm up the generator (for 4 minutes in this case)
slowly increasing the current is something I haven't tried yet, there are assistants to adjust charging current so there might be a way to accomplish this, albeit a little courser.

Is there already a fix for this?

I would like to have an option to increase from 0 to full load over the time of 15 minutes.

So that i van apply the load slowly on the generator.

Im new to Victron and playing around with node red so i have an idea to slowly adjust the input current limit after you started the generator.

Here is the code for ramp up. i shall made a code for ramp down too.

if (flow.get("ramp") >= 0 && flow.get("ramp") < 1 && flow.get("rampstate") == 1) {
    flow.set("ramp", flow.get("ramp") + 0.01);
    var ramp = flow.get("ramp");
    msg.payload = ramp * 25; // change 25 to your variable of max current draw
} else {
    flow.set("rampstate", 0);
    return null;
}

return msg;