How to mow undeveloped land?

Flail mower and it’s gone. Alternatively, the already mentioned sickle bar mower.

No farmer with the appropriate equipment in the circle of friends/family/acquaintances? With us, even a future neighbor came by with a tractor/mower before the construction started and flattened all the greenery. Afterwards, we chatted about the future neighborhood over a beer.

Renting sheep is also possible. The shepherd comes with the sheep and a fence and lets the sheep live with you for a few days. And just like that, everything is short and bare. :)

I actually did it with a scythe back then :)

Just a question for the scythe users. I have my excavation as a dune at the edge of the property. During the summer, I let everything grow because of the insects. Is it possible to work well on a slope with a muscle-powered scythe?

We simply had our property, which was at least just as overgrown, leveled with the excavator. Once very "fine" so that only a little soil was removed and all the green waste in between is left, and then once more roughly so that the soil can be used further afterwards and the property is prepared for the foundation.