+1 for tiptap, and yjs, used both to build https://www.buildmemo.com 's collaborative editor. Did not use hocuspocus but found it trivial to implement our own node ws backend.
So much this, really helps breakup complex tasks. Some examples off the top of my head:
If you have a function handling user sign up it often needs to build and write to multiple db tables. Split this into two functions a pure one that outputs the entities, and a second which takes these and handles writing them to a db inside a transaction. First the code is super simple to read, but more importantly it's easy to unit test since you don't need to mock anything, just make a list of input combinations paired with a list of expected outputs. Spend more time testing your business logic, less time verifying that postgres is working.
Transforming HTML into a pdf is trivial if you first iterate over the html and output a list of instructions that then get fed into a writer function one at a time, similar to how 3d printer instructions work.
Anytime I've done analysis work on a state that gets updated by a complex series of events it's always been worthwhile to build a discrete handler for each event type, then feed the events into it like a woodchipper. Complex problem solved with simple functions and a case statement.