v11 `Invalid Content-Type header`

The most recent update of v11 seems to break with:

Invalid Content-Type header. This request may not be supported by your tRPC Adapter, or possibly by tRPC at all

Invalid Content-Type header. This request may not be supported by your tRPC Adapter, or possibly by tRPC at all

Invalid Content-Type header. This request may not be supported by your tRPC Adapter, or possibly by tRPC at all

Invalid Content-Type header. This request may not be supported by your tRPC Adapter, or possibly by tRPC at all

The related commits in the rc.346 are probably:
- https://github.com/trpc/trpc/pull/5613
- https://github.com/trpc/trpc/pull/5652

I am using the react and vanilla fetch adapters, so according to the docs https://trpc.io/docs/migrate-from-v10-to-v11#explicit-content-type-checks-non-breaking my code should not be breaking

I went ahead and downgraded to

11.0.0-next-beta.318

11.0.0-next-beta.318

11.0.0-next-beta.318

11.0.0-next-beta.318 and it works fine