So for energy, a likely path will be the Dyson Swarm, meaning a cloud of orbitals. Many mistakenly think a Dyson Sphere was a rigid shell around a star. It never was. There's no material, actual or even theorized, that has the rigidity to sustain that. Because of that confusion, many now prefer the nomenclature of "Dyson Swarm" over "Dyson Sphere".

Dyson Swarms have the advantage of creating incredible amounts of living room and solving energy needs with relatively low tech (ie solar). They can also be built incrementally. A cloud of orbitals that capture the Sun's energy with orbitals between Venus and Mars will (IIRC) have a mean distance between them of ~100,000km.

Why is this important? Because the only way to get rid of heat in space is by expelling mass or, more likely, radiating it away into space. You can reuse waste heat to some degree but it's not perfect (because thermodynamics) and you can't totally avoid radiating heat away totally anyway. The wavelength of such radiation is entirely dependent on the temperature. At any likely temperature, that means infrared ("IR") radiation.

So a Dyson Swarm around our Sun would stick out like a sore thumb with a massive IR signature. There's really no hiding it. And we're capable of detecting it.

Conversey, there's really no hiding from any civilization capable of such feats of engineering. Plus any such civilization would be capable of sterilizing the galaxy out of any competition.

Mass follows on from this.