Black and blue are the important ones, they're the ones with the line voltage. From what I can see, they're both OK, and they have wagos on them.

Under normal circumstances, the grounding wire (green/yellow) shouldn't carry any voltage, but mistakes and faults happen. While you'll most likely be fine just covering it as it is, I'd give that wire some treatment too: If you don't have any wago clamps or similar, just snip off the exposed copper, and wrap some electrical tape around it just to be safe.

DISCLAIMER: I'm not in ~~Australia~~ Austria (I'm ~~European~~ Scandinavian), and I'm not a licensed electrician, let alone a licensed electrician in ~~Australia~~ Austria. I could be an internet terrorist who wants you to burn down your house for all you know.

Since you wrote you are in Austria, I'll write German as this topic is too important for misunderstanding.

Was du hier hast ist ein klassischer 230V-Anschluss mit 3 Kabeln:

• Schutzleiter PE (grüngelb)
• Neutralleiter N (blau)
• Phase (Schwarz)

Der Schutzleiter oder auch Erde führt in der Regel keinen Strom, sondern leitet Strom im Falle eines Schadens der Isolierung ab, bspw. damit dir das Metallgehäuse deiner WaMa keinen Schock verpasst.

Wichtig: Wie bereits erwähnt können Fehler bei der Verkabelung der Hauselektrik nicht ausgeschlossen werden - die Farben geben nur Hinweise, verlassen kannst du dich nur darauf wenn du mit einem Multimeter nach misst. Ansonsten musst du davon ausgehen, dass der freiliegende Kupferdraht Strom leitet.

! 230V Wechselstrom können tödlich sein !

Die beiden Leiter sind ordnungsgemäß mit einer Wago-Klemme abgeklemmt. Bevor du irgendwo rumspielst, unbedingt die Sicherung für die Dose rausmachen und auch den FI-Schutzschalter, sollte deine Wohnung einen haben.

Jetzt zur eigentlichen Frage. Ich bin kein ausgebildeter Elektriker und erzähle prinzipiell Unsinn, als random guy übernehme ich keine Verantwortung.

Das Ding sieht safe aus, mach dir keinen Kopf. Schau dass du die Dose zeitnah abdeckst wie bereits vorgeschlagen. Wenn das deine Badezimmer ist lüfte gut durch und lass da keine Feuchtigkeit eindringen. Das ist der selbe Anschluss, an dem du Deckenlampen anschließt. Nur an Drehstrom (E-Herd) darfst du als Laie nicht dran.

If you’re going to turn it on, you could put some wire nuts on the ends of each of the wires to keep anything from touching them. It’s always better to be safe than sorry, especially with electricity.

FWIW, here is the US, the ground wire is often completely exposed. As in, no colored jacket, just the bare copper throughout the entire run. Attached to ground at the breaker box, and attached to any grounding ports or metal boxes throughout the building.

Just call electrician, this is something where you don't want to cut corners.

Is there a reason you need to turn the breaker on for that circuit? Is it connected to a circuit like your kitchen or something?

In my opinion, if you aren't an electrician and can leave that circuit off until your friend or whoever can look at it, then just leave that circuit off. That is the safest approach.

Otherwise,so long as the wires are not touching and the black and blue wires are capped off and not touching bare metal, in theory you should be okay. Again, this is theoretical, it is possible that there may be something that I cannot see or think of that may cause a house fire by turning that circuit back on.

Put a cover on it like this (look for the right size, there are 2 - 3 different sizes)

https://www.bauhaus.at/schalterdosen/federdeckel-klein/p/12148379

You'll be fine. As long as the wires don't touch each other or get connected via some conductive liquid (e.g. water), nothing should happen. Cover it with something like electrical tape or some plastic cover for outlets just to be safe.

From my POV, I would say you are good. The dangerous blue and black wire are covered and yellow-green being exposed is not an issue. If you only have responsible persons in the house, you can turn it on without issues. You could also tape card board over it if you want to.

But keep in mind I'm not an electrician and give only my layman's POV.