Nik Collection 4 was released today (June 2, 2021) and the install procedure has changed. I found the steps at the following URL:
https://help-nikcollection4.dxo.com/install_activate
I hope this helps someone avoid the frustration getting the Nik Collection 4 installed to Affinity Photo. I was fouled up because I tried to follow the steps for Nik 2.5 and 3.0. However, the new release is installed for Affinity Photo differently.
Edit: By the way did a quick test and Nik Viveza worked fine.
Peace