Currently not much, at least not within the GUI. And before you do anything, you should understand the Cryptomator vault structure documented here.
That said: The error says basically, that an encrypted directory of yours is missing in the vault storage location. This can be caused by incomplete sync, but also incomplete delete-Operations. Cryptomator does not know, which is the case and cannot fix this. You can delete the folder /Users/…/…/…/Sonstiges/d/4C/5SC3XXTPGBXMLMUJ6HSMPOR7WGIUJA/k80GGLi3znvRA12NySF7gm63UTSojkJQ.c9r, but if the error was caused by improper synchronisation, you cannot access the content of the folder anymore when you unlock the vault.
This is ridiculous. After two months of usage, I have about 30 of these entries in the log file. You don’t get any info about the affected files/dir. So basically the software lost some files and is not telling you about it, or give you any insights.
And the community / devs in this forum also do not really provide help. This software is just dangerous!