FSI Start

Hi everyone, I'm trying to try out F# via FSI in VS Code (Windows 10)

I have Ionide for F# installed, and have used it before, but now every time I try to start it I get a message "FSI :Start resulted in an error", it goes on to helpfully report "the option has no value".

dotnet is in path, dotnet works great. FSI? nothing.

I also have the .net workload installed for visual studio 2022 (if that matters).

I started up my Linux VM (KDE Neon) fired up vs codium and tried FSI Start...same error! So no tinkering in f# for me tonight. Does anyone have an idea what's happening, across two environments? Google is no help...