Don't know, if this means file cached work or not.

It works.

I recommend to do several experiments with different Pafe buffers and FileSystemCacheThreshold values (Buffers > FileSystemCacheThreshold , Buffers < FileSystemCacheThreshold ), and check RAMMap. Try to do it with and without restart of  the computer.

If file cached worked, then there is something else that make Firebird runs slower on Windows 10.

Windows 10 is a desktop OS, and it demonstrates slowness in so many cases, caused by so many reasons, so I would not use it as a server, until there is no other choice.
I personally experienced slowness on one of my own desktops, and perfect performance on the another one. Better just stay out from this lottery.

Try to make experiments with Windows Server, it will make more sense.

Regards,
Alexey Kovyazin
IBSurgeon

Anto