(How does the app work? Think of the application as a file indexing system: you specify a folder on your local hard drive and the program will analyze the files (might take up to 30 minutes) and store metadata for it in a search-optimized datastructure.)

From what I understand most applications also separate frontend and backend layers and let the processes communicate via message passing over some form of channel and protocol. The solutions I found include Unix Sockets with gRPC (https://docs.microsoft.com/en-us/aspnet/core/grpc/interprocess?view=aspnetcore-6.0), local HTTP Servers with a REST API or gRPC, even JSON over stdin/stdout (https://github.com/xi-editor/xi-editor). Solutions for datastorage include custom file formats, sqlite databases or bundled mongodb instances into the main application.

I figured out the backend part with analysis running multithreaded and writing into a sqlite database. For the IPC I spawn a gRPC Server which clients connect to over HTTP/2. That way I compile a platform agnostic backend and platform specific frontends. It all works okish but I feel like it's unnecessarily complicated and there could be a common strategy I am missing.

*TL;DR: What are modern architectures for desktop applications equivalent to a microservice architecture with backend/frontend separation, message queueing, pub/sub, authentication, ...?*