I ran into this issue too. It's something to do with the types deep in the Firestore SDK and I can't find a solution to it other that to do multiple get() calls in a Promise.all

await firestore().runTransaction(async (t) => {

const [doc1, doc2, doc3] = await Promise.all([

t.get(docRef1),

t.get(docRef2),

t.get(docRef3),

])

// do stuff!

return Promise.resolve()

})