Game will fail to start when Spell Engine V1.0.5 and V1.0.4 is started with SodiumDynamicLights. The crash will blame SodiumDynamicLights however have not had the issue with other mods.

The issue is caused by SodiumDynamicLights.

txnimc/SodiumDynamicLights#9

Even tho this is not a fault of Spell Engine, this Dynamic Lights integration will be removed from Spell Engine 1.0+, to avoid crashing, as neither replacement qualify reliable, due to missing unique entry point.

not just 1.21, im crashing on fabric 1.20.1 as well

On 1.20.1, use LambDynamicLights, as it is specifcally supported by Spell Engine.
Other implementations are not, and they are not possible to be supported in parallel.

I think this might be relevant since you seem to have been willing to support the original mod: LambDynamicLights has been updated to 1.21.1, tho it has a little change in the API for the entrypoint to work.
And for the foreseeable future I plan to maintain it more regularly than the last few months.