Secrets Management with Firebase App Hosting and NextJS

You might like https://dmno.dev (full disclosure, I am one of the creators)

It lets you manage all your config and pull from various backends (like 1Password or an encrypted file within your repo). I have not built a GCP Secret Manager plugin yet, but it would be very easy and is on the roadmap!

Since a lot of your config is not actually sensitive (the NEXT_PUBLIC items), this would let you manage it within your repo, and toggle according to env or compose things together however you like.

It also provides validation, coercion, type-safety, leak prevention, and a lot more. Happy to help if you want to try it out.