Doomed

It certainly isn't just nouns, you do have classics like "zusammensetzen" (put together) and "verschlimmbessern" (to make something worse, despite attempting to improve it).

But yeah, I'm having a hard time coming up with a particularly long composite verb that still makes sense.
Usually, it's one word + a normal verb to kind of change the meaning of the verb, like "tanzen" means "to dance", and "seiltanzen" means "to walk on a tightrope" (literally: "to rope-dance").

And while you could theoretically extend it, e.g. as "hochseiltanzen" ("Hochseil" is a tightrope that's high above the ground; literally "high-rope"), we just say "auf dem Hochseil tanzen" instead ("to dance on the high-rope").
Or I guess, you'd specify that it's a Hochseil once and then say "seiltanzen" in the following sentences.

It can’t. German can only make compound nouns and even then it usually can’t combine multiple concepts. Instead, everything except the last component is there to specify what the last component is about.

Source: am German

no, thats not how composits work. Sure there are composite-verbs but they are rather limited (unlike composite-nouns which can become extremely long)

So I've heard. There probably are other languages that could work. ChatGPT says polysynthetic languages like Inuktitut, Mohawk, and Chukchi do. I don't have time to double check, but I'm sure if ChatGPT's wrong there are other examples where it's true.

Unfortunately, in 2025 they closed the loophole. You only can use the listed commands. And I notice the loophole didn't work for sending in either version of 5e (or in 3.5). It specifies a "short" message of 25 words or less, so while you could compress an arbitrarily long message into a single word (though possibly having to use some Morse code-type deal) it wouldn't help because it wouldn't be a "short" message.