It is unclear what file Nexcloud client Windows is syncing here but not a a single file is over 600GB
So what file is this and how to find out?
It says in total there are 2.2 GB to sync, so where is the problem?
If it blocks at this 2nd file, and you want to know which one, you can check the logfiles:
they can be quite verbose and you risk to have too much information.