Oze oh sorry I focused on the original issue and didn't even notice the latest message.
It seems like the way the migrations work Flarum will be unable to create composite primary keys in this circumstance. For reference, the migration in question
Creating the database locally and then copying it over would work around that issue. But the same problem will likely happen again when you install extensions 😬
I found this SO question https://stackoverflow.com/q/62418099/3133038 and this Laravel issue laravel/framework33238 . From the comments in those two threads it seems like people were able to simply ask DigitalOcean to disable the setting on their instance.
Laravel doesn't consider it a bug and the various workarounds described in the comments would require rewriting a large part of Flarum's migrations so I don't think we would add a special case to handle this.