I would definitely recommend Intellectsoft. It's a leading company in software development, they launch their projects, implement advanced technologies, switch to digital strategies, and, simply put, develop your business. They work with projects of any complexity. You can see their cases on the website, they are really impressive.
By the way, you didn't specify what industry your startup is in, but I can tell you in advance that https://www.intellectsoft.net/blog/best-android-frameworks/
works in many industries, including healthcare, construction, fintech, logistics, and others. Basically they offer a wide range of services, including IT consulting, enterprise application development, mobile and web applications, etc.