The Parker Solar Probe will make its closest approach yet to the Sun

If KSP is to be believed, this is shockingly difficult to do

In SpaceFlight Simulator it’s quite easy IIRC (it’s been a while):

1. Orbit yourself around low earth

2. When entering the transfer window (opposite side of the sun-facing earth, i.e. above midnight longitude) booooost

3. For orbit, aim for tangent with your target. For sun discovery, aim for sun center. Choose but don’t change.

The game is in 2D and you got nice auto-calculated transfert windows and trajectories. Is it one of those game simplification that makes it easy or there’s more difficulties?

The math is simple enough, it's just the delta-v requirements are brutal. Or you take the slingshot approach at which point the math requirements are brutal.

And I'm not aware of any KSP mod that helps you plan slingshots. And even if there was a slingshot maneuver requires a lot of precision because your ejection angle is highly sensitive to exactly how close you came.

The Parker probe was sent outward to Jupiter and used it to slingshot away much of it's energy. (We normally think of using a planetary encounter to gain energy but it works both ways. Ejection velocity from a slingshot at Jupiter can be anywhere from hitting the sun to solar escape. It's just most probes are heading out, not in.)