The mono team have deprecated xbuild and have made msbuild the recommended build tool. However, there is no msbuild package in Gentoo, and the dev-dotnet overlay is regularly broken. Since msbuild is now the defacto build tool for mono, I feel that it should be brought into gentoo main and maintained along side mono itself (perhaps through USE=msbuild?) Other distros bundle msbuild in their "mono-complete" packages.
I just revisited this issue now, and... is it still a thing that we actually need an external msbuild? I got mono working in vscode now without having a "native" msbuild, but just having dotnet-sdk-bin 7.0.200 installed. Can someone check, and maybe confirm/deny if it's working? Maybe you have to make a wrapper that calls "dotnet build" instead of "msbuild" in some cases?