For Reolink doorbell owners in the UK, there are some third party chimes that are compatible. I have just bought a Kerui wireless doorbell kit from Amazon. Its chime works perfectly as a second chime for my Reolink WiFi doorbell.

I also tried a Wesstun branded bell and chime kit. In that case the chime will pair with the Reolink doorbell, but when you try to use it there is a "memory full" error message from the chime, even though I reset it.

They both work on 433MHz but presumably there are slight proprietary differences in the signalling.