Ok, so in short - my hypothesis here (without knowing a lot about Synology systems and just going of what I can google) is that...
FUSE uses exFAT by default (or maybe is the only option, I am not sure as I usually work on Windows which uses Winfsp with NTFS format).
And Synology systems generally do not appear to support exFAT out of the box according to google. That would mean that DSM can't speak to the fusemount. In that case the error you see would make perfect sense.
According to google it should be possible to install exFAT support however. Alternatively FUSE might support an alternative format you can use on the mount. This I don't really know about as I don't use FUSE that much directly.
@Animosity022 Do you know anything more about FUSE's filesystem format on Linux?
Perhaps exFAT support was part of the prerequisites that the guide mentioned to install from
https://synocommunity.com/
But since I don't know what's in that package this is just speculation on my part. It would perhaps explain why this was not mentioned in the guide explicitly, so it's worth doublechecking that part of the installation again to make sure you didn't miss some part of it.
The command I gave you was just to verify that your current mount is in fact running on exFAT. Animosity can probably just tell us that though, so it's probably not a critical test to run.