I haven't seen the full preview stream or gone through the whole lead-up to the release of this route, but from the little I have seen, there hasn't been any mention as to why the DB BR 204 isn't at least layered onto the route, since it is the add on for MSB.
It's the first German DLC that I haven't purchased (reluctantly). I really like TSW 4, however this add-on is disgraceful. A boring and listless route with only one train and the recycled BR 363 (or 365, I don't remember exactly). Not even a new boxcar. The BR 204 (Rivet Games) is probably absent because it is an add-on that should be redone according to the new Tsw4 standards (for example currently it is not possible to create a livery for this locomotive in the CC, and it is a shame because there would be really many and beautiful). Too much work? OK! I got it. But in this state I WILL NEVER BUY IT. I am sorry.
It's probably been sidelined because it's the only TSW2020 loco that hasn't been updated to use immersive controls. It still uses the classic controls from 2020
I suspect the 204 has been abandoned not primarily because of control or LD issues, but because the physics are all wrong, and can't be corrected without basically redoing it from scratch. It effectively behaves like a diesel-electric, when it's a diesel-hydraulic. Which is a shame, because the visual 3D modeling is excellent (one thing Rivet have always done well), and also because it's the only German shunter in-game with the power to run local fraight in addition to yard work.
I mean, Skyhook has previously gone back and made an effort to improve their add-ons, I feel Rivet should do the same. I've not played Arosa for ages especially since the rush hour update messed with its physics, but I believe they went back and attempted to improve the loco from that.
She does have immersion controls. Just the introduction still uses the old scheme. But as some already pointed out: The loco physics are beyond repair and the sounds are a bad joke. My car is a better simulation of the BR 204 than this one from TSW. Which is, indeed, a pity because the visuals are excellent. BTW: I think she´s been spotted as AI loco on DRA ...