Save yourself the brain aneurism from watching anti-science 1990’s “perpetual motion” bullshit and look up “wood gasification (e.g., https://en.wikipedia.org/wiki/Wood_gas_generator)

Its not some secret or “free energy”. It is just converting energy from wood in a 2 step process -instead of burning it directly for heat, you extract the flammable gas, which is a more flexible energy source (and can be used in internal combustion engines like generators). Its been around for a long time. The Nazi’s even tried to run a tank on it.

Today, many large scale “biogas” reactors use similar mechanisms, though they typically use bacteria to produce gas rather than heat from partial combustion, which allows them to work on things that don’t burn cleanly, like garbage or sewage. I know a hobbyist that built a traditional combustion-based wood gasifier generator- it worked, but was a lot of work to keep the gas flowing and engine running. No free energy, you still need the (bio) fuel.