This is a weird choice of technical stacks, TBH. You never-the-less need to maintain two different frameworks, the UI component will be hard to look consistent,

This is a weird choice of technical stacks, TBH. You never-the-less need to maintain two different frameworks, the UI component will be hard to look consistent, and build/testing flows are probably different, and I have my reservation how much code can be actually shared, and to share that code what the cost you are paying. Better just use React all the way.