Code:
<GameInfo>
<Types>
<Row Type="UNIT_C6O_WORKER" Kind="KIND_UNIT"/>
</Types>
<TypeTags>
<Row Type="UNIT_C6O_WORKER" Tag="CLASS_LANDCIVILIAN"/>
</TypeTags>
<UnitAIInfos>
<Row UnitType="UNIT_C6O_WORKER" AiType="UNITAI_BUILD"/>
</UnitAIInfos>
<UnitCaptures>
<Row CapturedUnitType="UNIT_C6O_WORKER" BecomesUnitType="UNIT_BUILDER"/>
</UnitCaptures>
<Units>
<Row UnitType="UNIT_C6O_WORKER" BaseMoves="2" Cost="35" AdvisorType="ADVISOR_GENERIC" BaseSightRange="2" ZoneOfControl="false" Domain="DOMAIN_LAND" FormationClass="FORMATION_CLASS_CIVILIAN" Name="Worker" Description="Worker Unit." CanCapture="False" PurchaseYield="YIELD_GOLD" BuildCharges="100"/>
</Units>
<Route_ValidBuildUnits>
<Row RouteType="ROUTE_ANCIENT_ROAD" UnitType="UNIT_C6O_WORKER"/>
<Row RouteType="ROUTE_MEDIEVAL_ROAD" UnitType="UNIT_C6O_WORKER"/>
<Row RouteType="ROUTE_INDUSTRIAL_ROAD" UnitType="UNIT_C6O_WORKER"/>
<Row RouteType="ROUTE_MODERN_ROAD" UnitType="UNIT_C6O_WORKER"/>
</Route_ValidBuildUnits>
</GameInfo>
I even tried going to Steam\steamapps\common\Sid Meier's Civilization VI\Base\Assets\Gameplay\Data\Routes and tried for builders and it didn't work.
<Row RouteType="ROUTE_ANCIENT_ROAD" UnitType="UNIT_BUILDER"/>
<Row RouteType="ROUTE_MEDIEVAL_ROAD" UnitType="UNIT_BUILDER"/>
<Row RouteType="ROUTE_INDUSTRIAL_ROAD" UnitType="UNIT_BUILDER"/>
<Row RouteType="ROUTE_MODERN_ROAD" UnitType="UNIT_BUILDER"/>