Thanks for the warning -- some alternatives, in somewhat random but roughly dependability/activity/which I would choose order:
- https://github.com/netlify/netlify-cms
- https://github.com/strapi/strapi
- https://github.com/directus/directus
- https://github.com/tinacms/tinacms
- https://github.com/sanity-io/sanity
- https://github.com/wintercms/winter
- https://github.com/Camberi/firecms (tied to firestore)