Rob - You are describing a very common situation that many of us have to deal with all the time and there are different strategies for dealing with it.
There isn't any easy way to merge databases between environments. In general, the trick is to try and be clear in your mind about what is in the database (content) and what is stored in config files (configuration). All of the configuration changes that you make on your site that are stored in configuration files can be moved from your dev site to production site. But, changes to the database are not easily move from dev to production, so my strategy is to try to make those change directly on production and then copy the production database to my dev site.
- Code and configuration move from dev to prod
- Content moves from prod to dev
Sometimes, if I'm experimenting with content on dev, I just resign myself to the fact that I'll have to copy and paste it into the production site when I'm done. In the Drupal world, there are modules like Node Export that make it possible to export specific nodes from one site to another. It's not clear to me if this Backdrop version is working - you could test it.
I think this module will help you export menus from one site to another. Menus are in that grey area between config and content. The menu itself is config, but the menu items are content.
But, if you understand how configuration works you can create content types, fields, and views in your local environment and move them to production via config management. You just have to understand the difference between content and config.
Here is a good place to start.