Does the LSP provide clear autocomplete on what properties can be accessed on the bound _ ?

Asking as someone that doesn't use Scala at all, but has seen the hit-and-miss of some FP language LSPs.

Yes it does, otherwise the code would actually not compile.

IntelliJ or the older Scala-IDE for Eclipse certainly does, so I'd be very disappointed if the LSP impl (which the Scala maintainers have been pushing as the official IDE replacement these days) didn't.