I’ve found the relevant information
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Forum Thread: https://www.digitalocean.com/community/questions/how-to-add-my-digitalocean-app-as-a-trusted-resource-for-my-managed-database
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Feature Request: Page Not Found | Canny
I am engaging with our DigitalOcean contacts and will be drafting a PR to put a notice on our documentation about it. I’ll give the DigitalOcean team 7 days to respond to our internal convo with them before I’ll have the PR merged into the docs to make others aware.
In the meantime until this is patched (they see it as a feature request, security is not a feature 
) I would advise against using DO Apps + Managed databases and instead opt for a custom droplet.
Edit, draft documentation PR: Add warning about DigitalOcean MDB + App Platform by derrickmehaffy · Pull Request #331 · strapi/documentation · GitHub