@loach As far as I understand, App Platform is just a managed service. So you install things as “add-ons” much like you would if you were using something like Heroku. So it’s more building your infrastructure using a GUI, and Digital Ocean take care of everything behinds the scenes, which is why it’ll run more expensive.
Forge, however, is just an abstraction layer on top of Digital Ocean’s “traditional” offering, where you get a droplet and you can install anything you want on it. So it may be cheaper with Forge, because you’ll just connect Forge to a droplet and this its scripts will do the installation and configuration of services like MySQL on that droplet that you would otherwise be doing manually via the command line.
Digital Ocean don’t need to charge a premium for this, because it’s you doing the work and there’s nothing for Digital Ocean to manage, scale, etc. If MySQL on your droplet gets screwed up, then Digital Ocean leave it to you to figure out.