I’m no longer using it - I ended up going back to the Onedrive app, as it does selective syncing, but importantly, allows me to work on the same file as a colleague at the same time. I ran in to an initial issue with the M1 Mac Mini when Onedrive struggled when loading all the folders on initial sync (partly due me using it as an Arq backup destination, so there were a lot of files and folders for it to index). Once I deleted that, and it synced, I could remove the offending Arq backup folder from the visible file list in Onedrive and it synced fine.
I couldn’t use Onedrive in Mountain Duck, as my University blocked it from connecting. Oddly, Insync worked fine (and was able to access Sharepoint files).
However, if I’m really stuck, I now have it synced on my Synology using Synology Cloud Sync, so if M1 Onedrive gives me issues again, I’ll be able to continue working.