In the base game, there is a profession "between" the manual workers (laborers) and the knowledge workers (engineers) that still exists in the master branch called technicians (machinists).
Currently in the dev branch, the technician profession is removed (the decision was made a while back in an attempt to simplify), but as a consequence, most industrial building PMs need knowledge workers to function.
For individuals in a pop to become a knowledge worker, the education index of that pop needs to be at least 20%, which means countries that have very low education indexes are barred from using those PMs or buildings until they can raise their education massively, which takes 10-15 years even if the player is speed-running education.
The solution would be to reincorporate technicians into the PMs since they do not have this same education requirement. Since these technician pops would be paid more in buildings, they would more easily increase their education and thus can quickly become knowledge workers down the line.