The things I’ve tried to list here are jobs where you have a huge pile of bulk work that isn’t going to change much year to year. Some of the jobs might be dangerous, but I tried to list ones where that danger can be mitigated (vs. fighting in wars, which easily soaks up labor, but obvious downsides and much better suited to incorrigible prisoners).
Unexploded ordnance removal in Ukraine, Balkans, Indochina amongst others
Toxic site mitigations (unlined fly ash dumps, dredging, nuclear cleanup, etc.), oil and gas well decommissions
Munitions manufacturing, testing, and safing (especially in 2023 with depletion due to Ukraine)
Child care/adoption/orphanage clear-out
Basically anything to do with crippled or demented elder care
Water works like reservoirs (not too many dams left that make sense to build)
Developing world proper sewer systems (although many areas don’t have the economy necessarily to run the treatment plants that are needed to support underground sewering)
Bulk lab screening (medical or material)