What is the fundamental issue why you keep switching tech stacks?
I'm not an architect or senior developer, and not saying my take is better, but my considerations would be very different.
First, I would want to have a reasonably clear idea of what you want. My first idea when I hear 'stackoverflow for flash cards' is that you want collections of flash cards. I suppose you need some discovery mechanism, and ways for users to upload and share collections. You mention syncing, I suppose that means that every user always has the last version of a collection. What happens if a user deletes all or most of the flash cards in a collection? Will it be lost for the user or will (s)he be able to use an older snapshot of the collection. This would probably make things more complicated.
Then, I would consider the architecture. It is natural to go for a client-server architecture (and at this point I would draw two circles with two arrows pointing both ways between them). This simple architecture is enough for most applications.
The arrows in this diagram represent dataflow. The choices you make determine the actual data that is sent "over" the arrows. In this case you would need a strategy to distribute the flash cards and update them. So, you define the types of messages that the client and server need to handle and define some data structures for them.
So, the next step is to pick an implementation. An obvious choice for the arrows is HTTP. The client and server can then be implement in any programming language, not necessarily the same. The server can use some DB in the backend. So, again you need have some dataflow between db and server, so you can refine the diagram a bit, and define the data that goes over the arrows.
So slowly you can build up a detailed architecture. Note that it is mostly tech-agnostic, implementation should be possible in most programming languages and you can even make multiple types of client.
Even if you decide to redesign, with this method it is easier to keep your design clean and salvage some parts of protocols/structured that worked well enough.