How to let users allow other users to view specific node content? I'm using Drupal 9
I would like users to be able to allow other users to view their node content. Ideally a user will request access to view the content and the content owner will grant them view access.
How would I go about that?
I've looked at Nodeaccess, but it doesn't seem ready for Drupal 9 yet.
Node access user reference has nothing close for Drupal 9
You can do it using a small custom module.

Make a allowed users/node list (database table oe entity)
Implement hook_entity_access()
return AccessResult::allowed() or AccessResult::forbidden() according to your user/node table