1️⃣ Create an empty git repository named « Monorepo ».
2️⃣ For each existing "project_x" repository, move all files and folders (except .git) into a target path in the new monorepo, and then :
git commit -m "move all project_x files into /project-x"
git remote add monorepo MONOREPO_URL
git fetch monorepo
git merge monorepo/main --allow-unrelated-histories -m "merge project_x into monorepo"
git push mono