Seems like K2SO removed a tech:

Failed to load mods: Error in assignID: technology with name 'tree-seeding' does not exist. It was removed by Krastorio2-spaced-out.

Source: tree-seeding-selection (technology).

These two worked fine a few weeks back. :(

Hi,

I checked the source of the problem and wrote for the KSO2 author.

quick workaround: Disable "age-of-production" mod.
Disable "zen-seeding" in startup options, for Zen-garden.
After this you can enable age-of-production again.

Here is the details:
https://mods.factorio.com/mod/Krastorio2-spaced-out/discussion/699c2063e7ee769946935fd3

Hello!

Thanks for the quick reply; will this have any effect on the Zen-garden afterwards? Zen seeding being disabled?

Zen seeding, is an amount of extra seeds, for each tree, they are only different in visuals after planting, so it is more of a cosmetic extra.

All recipes use basic tree-seed if disabled, and K2 should have it's own tree variation recipes to replace them.
Zen-tree (planting box versions) will be still available.

You will have full functionality, and in case, you want your trees to look different when planted from basic seed, you can enable mod: diversitree

Yes, thank you, I already have diversitree. :)