I'm actually amazed that this piece of shit wasn't charged with terrorist acts.
As I've already explained, there are very few articles in the German law that explicitly refer to terrorism, like financing terrorism or creation of a terrorist association, and so far none of them seem to apply here. There is no charge of just "terrorism", but the motive (such as terrorism) behind charges such as murder does of course affect the severity of the punishment.
And I think I need to say that again: the investigetions are still far from completed, it will probably be weeks if not months until the opening of judicial proceedings. We do not know yet what the final list of charges will be. Until then, it's perfectly reasonable to keep him imprisoned under the charges of murder, attempted murder and assault which were unquestionable from the start.
What do you mean by that? That he didn't 'prepare' for the attack? Other than proclaiming multiple times in social media that we was going to do this, that caught the attention of multiple people other than the fecking police, eventually unless Germany changes it's stance on immigrants and Muslims in particular.
That's not how those laws work. It's a charge specifically for acts that were not brought to completion, or for assisting in preparing acts. You don't prosecute both the murder and the preparation for that very same murder, for example.
Of course it matters. If a muslim did this all on his lonesome, links would be made with all kinds of extremist Islamic organizations that he probably agreed with explicitly somewhere in all of his social media posts - and he would be described as a muslim terrorist that supports ISIS or Al-Qaeda or whatever. Cause those organizations are already classified as terrorist, so it's quick link to call it terrorism - and possibly a terrorism charge. (If 'waffen/weapon' in article 89a(2)2 of that law can be interpreted as a car.)
§89(2) is referencing the weapons listed under (1), and the list there makes it very clear that cars don't fall within the scope of that law.
Your theory that muslims are treated differently in terms of being charged with "terrorism" does not hold water when you compare it with last year's planned terrorist attack on a christmas market to "kill infidels" by a 15y/o which thankfully did not come to fruition. He has been
sentenced for collusion to murder, disturbing the public peace by threat of a felony, and the use of symbols of a prohibited organisation. The court's statement makes it undeniably clear that they planned a terrorist act and are being judged for them, but the articles they are charged under by themselves don't state it as they are umbrellas that terrorist acts, but also other acts fall under.
That is similar to how it has been in another recent-ish case, the attack on a synagogue in Halle in 2019. There is no doubt that it was case of terrorism, both the wording in the court and in the media leave no doubt about it being seen as such. But the charges were murder, attempted murder as well as incitement to hatred (Volksverhetzung).
Again, as stated above, terrorism is a motive behind a criminal charge, not a charge itself except for very few cases like "financing terror" or "creation of a terrorist organisation". That's just how things are in German law, there are no different laws for murder out of terrorism, for personal gain, out of racism or whatever, there is just murder with a motive of X, Y or Z, and those motives are then also considered when defining the sentence. In a few cases the motives behind an act even change the charge itself, like the difference §211 (murder) and §212 (manslaughter).
Again, a "terrorism charge" in itself is not a thing that exists in German law. Doesn't matter if we're talking rightwing, leftwing, or fundamentalist terrorism.
You're correct in that security apparatuses in Germany (and elsewhere) are generally (far) right leaning, we're usually saying here that the agencies are "blind in the right eye" (auf dem rechten Auge blind). But that's a problem in everyday prosecution in the laws, not within the law itself. Would the equivalent of the public threats he made be issued by an islamist or a leftwinger have gone equally unpersecuted, the warnings about them gone equally unheeded? I won't say it's impossible, given just how overloaded, undertrained and badly connected German police and other agencies are, but I'd say it would have been way less likely. But the laws itself would have allowed for it regardless of which political or religious orientation they are a part of.