I solved a portion of this issue. A major challenge here is that tutorial code is frequently outdated.
But the error I was receiving is not related to this, or any issue with Realm, but an issue with my server code.
I’m using Mongoose via a node backend. I’m also using mongoose-unique-validator to ensure a unique email for each user. It turns out that this validation fails on db access errors. So my backend was receiving db access errors, but they were manifesting as ‘Name already in use’ errors.
I discovered that my database user, found under Atlas > Database Access did not have the correct permissions, breaking several of my database interactions. Editing my user to change ‘database user permissions’ to ‘atlas admin’ resolved the errors.
My server code had been functional previously. So not sure what happened there.