Globally, manual workers far outnumber knowledge workers. However, it’s true that you could lure most subsistence farmers to factories with high wages and then use tractors to farm the land (demand for food would go way up with the increased global incomes, though this might be mitigated eventually with plant based/cultivated meat). I think many knowledge workers would take lower unemployment/UBI rather than becoming manual workers. So I still doubt you could double the manual workforce quickly.
Globally, manual workers far outnumber knowledge workers. However, it’s true that you could lure most subsistence farmers to factories with high wages and then use tractors to farm the land (demand for food would go way up with the increased global incomes, though this might be mitigated eventually with plant based/cultivated meat). I think many knowledge workers would take lower unemployment/UBI rather than becoming manual workers. So I still doubt you could double the manual workforce quickly.