If you are running an older Mac (e.g., macOS High Sierra or Catalina), official updates may be greyed out in the App Store. Community-tested workarounds include:
As Apple released newer versions of Pages and Numbers, they began requiring the latest macOS (like Catalina or Big Sur), effectively locking out users with older MacBook Pros and Airs. The Missing Link: all apple iwork 20142017 patched
Legitimate sources: