The domain logic is like there are a bunch of objects, as well as a lot of configurations, according to ddd, there should a base entity, as well as dtos, using entity framework code first, always use migration to mysql, each change will be displayed timely. Mongo DB is a general object store, to save front end dynamic data, it is possible to save items with different and mutable properties into the same collection, which makes the whole form dynamic configurable. References can be as in database, using foreign key constraint, and lazy load collections.
OOP design is not hard, for each config, there is a tree, which consists of dynamic control nodes, and expanding the tree and resolve controls into mysql, then save the mutable whole config tree into Mongodb can be a good solution. BTW. It is not hard to find a mongodb visualizer adminMongo management portal on Github, simply config connection, and visually see all data in collections and do operations. Could be good enough. Based on an ABP framework.
Suddenly find my explanation on expanding encapsulating a tree can be critical. Really impressive in recursion.