According to Scala style guide (https://docs.scala-lang.org/style/files.html), multi-unit files should be named with lower camel case. However, nobody seems to do it. I asked few experienced Scala developers and they didn't know about this convention. Even mentioned example is misleading and Option.scala (checked for scala 2.13.6) starts with capital letter.
This whole idea is for me rather obscure. On one hand official style guide states that as
very important convention
on the other hand even files built-in Scala language don't follow this convention.