Additional brass instrument "Baritone horn (Central Europe)" for the list of instruments.

Sorry, Bb1–Bb4 of course. It is the range given on the German Wikipedia page. The low notes can be played safely without being a professional. Of course not everyone can play the high notes. Is this indicated by the different note colors in MuseScore?

In the German Wikipedia the same range (Bb1–Bb4) is given for the baritone horn (CE) and the euphonium. In the English Wikipedia a range of (A1)Bb1-E5(A5) is given. However, I have noticed that the graphic file with the range has "bassoon" in its name. This seemed strange to me and I stick to the German Wikipedia. I don't know what the precise "demarcation" between amateur and professional in MuseScore is based on (on this Anglo-Saxon system of levels, which says exactly what you have to be able to master in level X?) Normally, lower tones make less problems on brass instruments, at higher levels it becomes difficult. From E2 to G4 you should be able to play as a (good) amateur. Bb1 is a natural tone (without valve) and can also be played on the baritone horn (UK), euphonium, trombone, tenor trombone (Bb1 is red in MS on these instruments). The following notes up to Eb2 require a 4th valve. Almost all baritone horns have a 4th valve (also allows alternative fingerings for better intonation), so these notes should also be olive green. There are certainly brass players who go beyond Bb4. Theoretically everything is possible, but at some point a note like this doesn't sound good anymore or sounds like a dog whistle.
So my suggestion would be:

Looks good. For the tenor horn (CE) and euphonium (also applies to trombone and tenor trombone) the Bb1 should still be olive green. It is playable as a natural tone on these instruments. On a euphonium with 4 valves (not rare) the otherwise missing notes B1 to Eb2 are also playable (→ olive green). Apart from this, B1 to Eb2 can be played by good brass players as so-called false tones even without the 4th valve (But this is difficult, red is OK.).

I know ;o) I only noticed it in comparison to the well defined baritone horn (CE). Of course this would be a different issue. By the way, on the French Wikipedia page the same range is given for the euphonium as on the German one.

Since the list of musical instruments is a list of the world's musical instruments, differences in usage and naming must also be taken into account.
If a future Musescore version had the option that one could specify a language for the instrument names in scores (i.e. independent of the GUI language), one could possibly approach such naming problems differently. This would be useful either way, for example, if you are transcribing baroque music and would like to have Italian names, or for brass bands, English names, etc.
As for the baritone horn (Central Europe), there is an extensive German-language discussion: https://musescore.org/en/comment/981167#comment-981167
The Anglo-Saxon baritone horn is not the Central European baritone horn, but the tenor horn there, which has a different ambitus. I also wonder where the problem is, since primarily the general instruments are displayed, which shows only the most common instruments and is therefore very clear. Perhaps you can elaborate on what is so confusing about this?