First off great mod and love playing with the advance modules.
I have come across an issue and dont know if its a bug or by design.
Solar panes and accumulators when being built in assemblers are not affected by any productivity modules. Is this by design?

Thanks for the compliment on my mod, glad you're enjoying it! You're correct, in Factorio productivity modules usually only affect intermediate products. This is not a bug but rather by the game's design. However, in my mod, I've included a 'God Module' that bypasses these restrictions. With it, you can get productivity bonuses on solar panels and accumulators as well.

Thanks for the quick response. I know that there are a lot of assemblers / products where you can't install productivity directly into the assembler. But you can beacon using the mods productivity beacon and install prod mods and it would affect the assemblers where no prod mod could be installed. This works fine for all other products except for solar and accumulators.
In the below images you can see 2x assemblers in an 18 beacon build. One assembler gets all 18 (2160)% while the solar gets only the 3x speed beacons and zero productivity.
https://imgur.com/a/2vpJhWe
https://imgur.com/a/TLIOAip
I haven't unlocked the god modules at this stage. But am i correct in that they will not be installed in beacons only the assemblers.
Either way it might be back to the drawing board on my builds and some testing.

Edit: Should also add when using max rate calculator the calculator includes the 2160% productivity bonus for theoretical output on solar

Thanks for your detailed response and for sharing the images. It's important to note that my mod was a small hobby project, so there might be some limitations. Regarding the Max Rate Calculator, I'm not sure how to adjust it to include the productivity from beacons. It's also key to remember that, in Factorio's design, low density structures are considered intermediate products, while solar panels are finished products. This is why, by default, they don't receive productivity bonuses.

Small hobby project..Sill great work.
After doing some testing you are correct that all intermediate products receive the productivity bonus while all finished products dont. Despite what throughput calculators like "Max rate" advise.
I suspect that there is a script in the source code of the base game that specifically is set to ignore productivity bonus on all end products.
it may require a second mod with new assemblers / recipes as outlined here: https://forums.factorio.com/viewtopic.php?t=61822

Thanks for helping me understand the mod better. Now to go back and rework the builds

Just thinking out loud here as i really dont know a lot about modding but i have found this mod that uses a simple script to overrides the base game limitations for productivity. Could the same thing be applied to end products?
https://mods.factorio.com/mod/root-prod-beacon
for k, v in pairs(data.raw["beacon"]) do
v.allowed_effects = {"consumption","speed","pollution","productivity"}
end

EDIT: Problem solved
https://mods.factorio.com/mod/zzz-productivity-4-all
Now for some totally unbalanced game play