The problem with the capital Russian letter "I" in NextCloud (OwnCloud), how to solve?

Question

Character encoding

I install a cloud service on my hosting (OwnCloud = NextCloud)
The installation goes well, I start working and I notice the following thing:
When downloading a file containing a large Russian letter "I" in the name, the entire list of files on the cloud ceases to be displayed in the web interface, suggests contacting the administrator .
The same is true if a file with a name containing the Russian capital "AND" appears in the folder specified as synchronized in Windows (via the OwnCloud or NextCloud application) - it is not uploaded to the server, the error "The file contains invalid characters in the name" appears, and after that, the list of files with a suggestion to contact the administrator is not shown in the web-face either.
I tried:
changing the encoding in the MySQL database on the hosting - does not help.
Where to dig, how to be, who will help?