I can’t add the Cryptomator vault to Windows 10 Search for index.
How can I do it?
In general, a Windows machine does not allow indexing of network shares.
IF the network share is a NAS or a server or an other machine, then you can enable sources from there to your searches, but the indexing is done from the source machine and it just gives back a index file.
As the cryptomator vault is not a NAS or a server or an other machine, you don’t have the option to “Allow files on this drive to have contents indexed in addition to file properties” in the properties of the drive.
Details: https://www.online-tech-tips.com/windows-10/add-network-folder-to-windows-search-index/
Hah… But, Archivarius 3000 can do it… This program sees any Cryptomator vault (Web, Dokany) like a disk…
Sadly, I do not want to use any third-party programs.
Developers need to do something about it …
But: Archivarius is an indexing solution. Cryptomator is not. I’m pretty sure that archivarius does not encrypt files for online storages. 
What? 
I wrote about the search in encrypted vault.