I thought I would give OneDrive backups a try again, but I’m still facing the same known error:
Is there an alternative out there that will allow me to backup my OneDrive files to my TrueNAS server?
It works for me.
Using OneDrive personal - not linked to O365 account (I don’t have one of those)
Been there, done that 
Had the same issue with Dropbox and with OneDrive.
I don’t know if it is the TrueNAS API causing unnecessary much api calls or Dropbox and OneDrive being cheap. Either way, you will run into API limits pretty fast on both.
Solution for me was to sync Dropbox to a client and from there robocopy it to TrueNAS.
No issue here backing up my OneDrive for Business to my TrueNAS daily. It’s worked fine since the new python script was introduced a while ago.