I ran into another problem that the AI workers don't do any area formatting. Could this be related to their incomplete employment?
In order for the AI to use a worker-unit(s) properly (i.e. for the AI-strategy 'Terraform' to be applied to that unit), the unit must have
all the 'terraforming' abilities checked. But that does not mean the worker-unit can immediately use all of those abilities.
Worker-jobs can be unlocked with techs, with (Strategic) resources, or with a combination of those. For example, in the epic-game, 'Build Fortress' requires the tech Construction, but 'Plant Forest' requires Engineering, and 'Build Airfield' requires Flight — so even though all Workers effectively have those 3
potential abilities at the start of the game, they are unlocked in 3 different ages. Similarly, 'Build railroad' requires learning Steam Power, but also the resources Iron + Coal, so nobody can build rails unless they have satisfied all 3 conditions.
So if you want specific races to have access to specific Worker-abilities, then one option might be to tie the Worker-job(s) you
don't want them to have, to a specific Resource (or better, a combination of resources) which that race cannot access (but other races can).
e.g. If Elves must not cut down trees, then the 'Clear forest' ability (and maybe also the 'Clear wetland' ability — or you could assign the 'Clear Forest job to Jungle terrain) could be made to require Iron (which, as we all know, is poisonous to Elves) -- so you could set up your tech-tree to prevent them from seeing Iron in the first place, e.g. by making it appear using a prerequisite (starting) tech of 'Detect Iron-ore' that the Elves don't have, but that everyone else does.
Conversely, the Dwarves might need Iron for their mine-carts — but if you don't want anyone else's Workers to be able to mine tiles, then you could make a 'Mining' tech which cannot be traded, and which can only be researched by the Dwarvish clans, e.g. by (also) giving it a prerequisite tech of 'Being Dwarvish' — which only the Dwarven clans are given to start with.
(But note that if your mod has more than one Age, any techs which cannot be researched by all tribes, cannot be 'Required for era advancement').
And if there are any Worker-jobs that you don't want
anyone to be able to do, those can be tied to a dummy resource/tech that no-one can see/learn (like in the Mesoamerican Conquest scenario, where the 'Build rails' Worker-job is tied to the 'Guinea-pig'[?] resource -- which doesn't appear anywhere on the preset map)
Basically, you need to Venn-diagram the Worker-jobs, to figure out the best way of assigning those abilities only to specific groups.