I'm curious about this part: "The Notes formula language was good ish for the time but really became very dated, and the alternative LotusScript was a dead end too."
IIRC LotusScript was basically VB but with a different object model. Why was it a dead end?
Back then a lot of software particularly in the windows world wasn’t very good at talking to anything else. Today everything talks to everything.
Notes already had so many problems it was sunk and lotuscript which as you say was like script. Good but not enough to stop the titanic hitting the iceberg.
It wasn't that hard to get data out. IBM released a native Windows ODBC driver for Domino databases. Since the underlying database was non-relational you couldn't really use it for SQL queries with complex joins but for basic data export tasks it worked fine.
Java became available as an alternative to Lotuscript on the backend, I believe in version 5, and Javascript was made available on the frontend around that time. Although maybe I'm thinking of the web version of the frontend.
It was very hard to get data in and out it had almost no capability for data import/export.
Internet email killed Notes early advantage as one of the first email systems.
It was a very closed environment hard to connect or program outside its own sandbox.
Sharepoint was a full on assault by Microsoft on the groupware category and its enormous success was at the expense of Notes.
The web did many things better than notes there much much overlap.
The UI was clunky in some ways.
Some of the concepts like replication were just too much too early for many people to grasp.
SQL rose in the corporate world chipping away further at notes.
The Notes formula language was good ish for the time but really became very dated, and the alternative LotusScript was a dead end too.
Unstructured document databases were very polarizing sine people hated them with a passion.
The parent company Lotus main product 1-2-3 which ad dominated the spreadsheet world got smashed by Excel.
There’s more reasons too but there’s enough there you can see the doom of Notes.