Memory compatibility check

will this work as an upgrade for the memory for the PR4100?

See the dedicated subforum for the PR series where people more knowledgable with that device may be able to assist.

https://community.wd.com/c/network-attached-storage/my-cloud-pro-series/214

Generally the My Cloud subforum discusses the single bay/single drive My Cloud which does not have user replaceable or user upgradable memory.