At the end of the Geas spell description it is stated that
You can end the spell early by using an action to dismiss it. A remove curse, greater restoration or wish also ends it.
So the question is: is the spell Geas dispelled by Dispel Magic?
When it is casted using a spell slot of 9th level, the spell is permanent and
lasts until it is ended by one of the spells mentioned above.
Once again, is it ended by Dispel Magic in this case?
The description of Dispel Magic is as follows:
Note that it specifically says it can end any spell. Geas doesn't provide any exception to this; it just says that it can be ended by the spells you listed. Compare it to, for example, Forcecage, which includes the following line:
If Geas was meant to be impossible to dispel with Dispel Magic, it would include a similar line.