>Did IBM try to rewrite it from scratch or something?

In a way yes, IBM wanted notes to be an email clone. IBM took cc mail (I think) and shoehorned it into Lotus notes.

To me, that ruined Notes. If I get the versions numbers right, version 3 was great, IBM/Lotus came out with v4, which to me was a bit worse, and each new version was worse than the prior. Instead of focusing on emails, IBM should have focused on making notes servers easy to install and maintain and keep the application portion relevant.

By worse, it was the application portion that degraded. If you saw how cool the applications were with v3, you would wonder why Notes never became a "thing". Even third parties were creating applications for Notes at the time, some were very good. But to me IBM ruined that business by focusing on only Email part of Notes. Now AFAIK, there are no 3rd party applications for notes.

Maybe the company that bought notes from IBM is trying to get back to the roots, but I kind of doubt it.

The IBM Lotus Notes mail client and cc:Mail were developed independently by separate teams in different locations. Both were originally built by independent companies that were later acquired. cc:Mail was killed in 2000. IBM might have added some Notes features to achieve functional parity with cc:Mail and make it easier for customers to migrate.