I'd say some form of alert when you login of changes that you can read more up on, link to examples or video etc beyond release notes.

Could see when last logged into and with that be able to pull changes that are new from that time and now.

That way, you have the information alerted at a point the user will not miss and from there they are aware to read up more or not if they like.

Email's are nice, but be shame not to have that information more tailored at point of interaction. That way if a user login say 6 months later they would be advised of changes since last logged in, compared to going thru how many emails that build up and end up getting filtered into some folder hardly viewed.

But the ability to view changes from a point outside the release cycle of changes allows somebody to glean what is new for them and if case of some feature tried and then withdrawn during there last login then no need for them to even read about it as moot to them. Sadly many release notes gear towards having read all the previous, even ones that later get superseded.

This also avails the ability to alert to changes when the user approaches those options and if some subset they do not use then they won't need to read upon those changes as a priority. But that is another angle of approaching how changes are communicated to a user.