Desktop Links, Icons are gone

Dear Community, I have a very strange problem with the nextcloud client. After installing this on Windows 11 23H2 and also Windows 11 24H2 all *.lnk Icons on the Desktop and also the Taskbar are white. The next problem is that adding an attachment in Outlook by browsing the local PC is also not working, Outlook hangs. Please help me to fix the problems!

What exactly did you sync with the client? The whole /Users/username folder?