Unity is replacing its scripting runtime. Not tweaking it, replacing it. The Mono runtime that has sat under every line of C# you have written in Unity for years is being retired in favour of Microsoft's CoreCLR.
Source: [Dev.to](https://dev.to/oceanviewgames/unitys-path-to-coreclr-what-the-mono-cutover-means-for-your-studio-49p1)