mods not loading settings are defult and no pending mod updates keep geting this error thought it was incompatable with another mod
so i disabled all mods and activated them 1 at a time seems to be a compatibility issue with 5dims core

Failed to load mods: Kux-OrbitalIonCannon/data-final-fixes.lua:13: attempt to index field 'orbital-ion-cannon' (a nil value)
stack traceback:
Kux-OrbitalIonCannon/data-final-fixes.lua:13: in main chunk

thanlk ypu for your investigation, but there is a mistake
yes, the error only occurs when 5dim_core is installed, (because the if) but the cause can be another mod.

if mods["5dim_core"] then 
    data.raw["radar"]["orbital-ion-cannon"].next_upgrade = nil

data.raw["radar"]["orbital-ion-cannon"]. is missing because it has probably been deleted.

i have installed 5dim and all my mods and the error does not occur with it.
https://prnt.sc/pLxSpg6hZGTm

how do i fix it?

sorry i thought that was clear.
find out which mod deletes this. You had already started looking.

5dim core... its the only 1 tat causes this error and u said u got them running togather

sorry, it is not possible to search for an error that does not exist (at my game)
as long i don't know who deletes the prototype i can nothing do.
Yes, I could intercept the error, but that doesn't restore the prototype needed to build an ion cannon. and would lead to other errors, none of which I can test because the first error does not occur.

Try a clean install. delete all mods, then add 5dim and ion-cannon.... that's what worked for me.

Same Error. and also tested With ONLY:

base ( No DLC )
5Dim's mod - New Core
Kuxynator core lib
Orbital Ion Cannon

Problem is might be indeed in 5dim core.

Also git issue on 5dim. https://github.com/McGuten/Factorio5DimMods/issues/105

sory i have already invested a lot of time to find a solution. i don't have any more time.