The creator of Advent of Code does not want the inputs to be leaked. That's why they are in private git submodules.
git clone --recursive git@github.com:DerEmperor/AdventOfCode.gitif you forgot the --recursive:
git submodule update --init --recursivegit submodule add git@github.com:DerEmperor/AdventOfCodeInputs2026.git ./2026/inputsgit submodule init
git submodule update