The resharper-fsharp uses Fantomas under the hood to format the source code. No need for any additional plugins.
From Rider 2022.2 onwards, Rider can detect your
dotnet Fantomas installation, either globally or locally.
Install Fantomas locally with:
dotnet tool install fantomas
Prior to Rider 2022.3 it did not respect the default settings of Fantomas.
If you are stuck on version 2022.2 (or earlier) consider adding the default settings of Fantomas to your