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Max the relations with a major faction (stalwarts, pilgrims) to Devoted and pick the "More workforce" bonus multiple times during rallies of support.
You may also need to pass some laws like "Childhood - Apprentices", "Youth - Dutiful/Liberated", "Outsiders - Allow Productive", "Parenthood - Communal" and use the city ability from Youth law.

Unclear if automaton events also help with the worker ratio.