Exhausting internal heat happens because the isotopes capable of radioactive decay have spent their vigor. But you could bring back volcanoes via tidal heating.
Tidal heating (also known as tidal working) occurs through the tidal
friction processes: orbital and rotational energy are dissipated as
heat in the crust of the moons and planets involved. Io has a similar
mass and size as the Moon, but Io is the most geologically active body
in the Solar System. This is caused by the heating mechanism of Io.
The major heating source of Earth and its moon is radioactive heating,
but the heating source on Io is tidal heating. As Jupiter is very
massive, the side of Io nearest to Jupiter has a slightly larger
gravitational pull than the opposite side. This difference in
gravitational forces cause distortion of Io’s shape. Differently from
the Earth’s only moon, Jupiter has several moons (i.e. Io, Europa,
Ganymede and Callisto). As Io is the innermost moon of Jupiter,
Jupiter pulls Io inward and other moons pull Io outward. This causes
Io’s orbit to be elliptical and eccentric. The distance between
Jupiter and Io changes all the time and the distortion of Io likewise
changes all the time. The constant change in the shape of Io results
in a large amount of friction in the moon and the friction-induced
heating drives strong volcanic activities on the surface of Io.
If your planet has company capable of gravitationally flexing it back and forth, that will heat it up and restart some of the geologic processes which on Earth are driven by a molten core.
A different scheme to fire up your planets tired cold core might be inductive heating. A planet with a conductive core traversing a strong magnetic field would heat the core and power up geologic processes. Clearly inductive heating is a thing but I could not find that it is known to happen to any planets. That was my answer to Can you replace a sun with a burning moon?