How do I go about creating an interesting progression for metal refinement for my automation RPG? [closed]

Looking at other games, there are a few factors that can be played with.

-speed
The speed at which a refiner can process inputs and produce and output. For most players, I think this is the core value expected to improve with higher tech refiners. Example: ARK has a refining forge and an industrial refining forge. The only difference is that the industrial forge smelts far faster at the cost of more advanced fuel and more space.

-yield
The input to output ratio is another important value. If you input X ore and get Y ingots, then higher tech refiners will typically get a value for Y that is closer to X than a lower tech refiner. The yield should never be more than 1 unless magic is involved (mass out can't be more than mass in). Example: ARK mortar and pestle vs chemistry bench. The chemistry bench has a higher starting recipe cost, but produces more items per use than the equivalent items would in a mortar and pestle.

-Refinable Materials
The types of materials that can be refined can be another good option for differentiating. I would recommend that you not go overboard with limiting refiners to a small subset. In general, as the tech level goes higher, the refiner should handle all previous inputs plus a few new ones. Example: Space Engineers survival kit vs basic refiner vs refiner. The survival kit can only process stone, but lets you get the materials you need to get a basic refiner, which can refine most ores. Those ores let you craft a full refiner, which can refine all materials in the game.

-number of inputs
If you want to get more complicated with alloys and exotics, more advanced refiners can have more input slots available. Putting different combinations of inputs results in different outputs. More input slots, more combinations, more advanced.

there's just too many options

You don't need to add every single refinement to the game. Adds only refinement that is actually used to craft item in your game, and if you can, choose refinement that cover as much item as possible to reduce the amount of refinement.

and most of them are far too complex to consider for a game that's supposed to be accessible.

You can try not adding the "far too complex" refinement to the game and instead sell the refined item from merchant. You allows player to sell raw material for money, and then player use the money to buy the refined item. If you insist for the refined item to be unlocked before player can have access to it, you can try making the merchant ask for additional material (probably one of the base material to create the refined item) alongside money, and lock that additional material behind progression, so that player don't have access to the refined material before they unlock the additional material.