Downsides: lack of jobs, libraries, learning materials, small community, little promotion by Microsoft outside of "what's new in F#" and other announcements.

It's a shame because F# is a beautiful language — it's fun to read, write and maintain. .NET now works well cross-platform with editors other than Visual Studio. General perks of .NET like cross-platform compilation are a nice bonus, for example, on macOS I can:

    brew install dotnet

    dotnet new console -lang F# -o HelloWorldApp

    cd HelloWorldApp

    dotnet publish -c Release -r osx-arm64 --self-contained

    dotnet publish -c Release -r osx-x64 --self-contained

    dotnet publish -c Release -r win-x64 --self-contained

    dotnet publish -c Release -r linux-x64 --self-contained

To get self-contained binaries (that don't need .NET to be installed locally) for those platforms.

There is a decent multi-platform UI framework called Avalonia: https://github.com/fsprojects/Avalonia.FuncUI

There are good actively maintained web frameworks: https://fsharp.org/guides/web/#web-frameworks

There are some passionate people writing great books about F#: https://fsharpforfunandprofit.com/ddd/

Most of F#'s adoption issues seem to be because:

1. It's tough to convince people outside of the .NET community to use .NET.

2. Most of the people using .NET use C#.

3. It's hard to convince C# users to adopt F#. (See https://www.reddit.com/r/dotnet/comments/16m0wdj/why_dont_yo... and similar threads.)

I'd love to work with F# full-time, but — short of starting my own company using it or convincing Microsoft to pay me to help them showcase its benefits — it's been hard to find work with F#, which drove me to spend time with other languages.