Currently, above code works if you use eth_signTypedData. As such, the quick and dirty way to go about it is to monitor MetaMask releases to update your dApp to use eth_signTypedData_v1 once it’s supported.

A more elegant solution would be to gracefully handle the errors it throws to use eth_signTypedData before the changeover, and eth_signTypedData_v1 after. Untested pseudocode:

try signing with eth_signTypedData_v1
if it fails, try signing with eth_signTypedData