I find it odd that you've struggled so much with generating API clients. I've generated C# and TypeScript (Angular's HttpClient and React Query) clients for my API and never had any issues with them. With that being said, I didn't use OpenAPI's Java-based code generators and rather used ones made by third-party developers such as NSwag[0] and openapi-codegen[1].
[0]: https://github.com/RicoSuter/NSwag
[1]: https://github.com/fabien0102/openapi-codegen