In the meantime I still haven't done any project with nullable references, because the ecosystem has yet to move along. Same applies to ValueTask for async code.
Which part of the ecosystem is blocking your projects from using nullable references? I find them very helpful, but the projects were all newer or migrated to new SDK.
It is relatively easy to find corporate libraries, or commercial products that still aren't using it, including Microsoft products still stuck in .NET Framework, or .NET standard 2.0.
If you want name shaming of commercial products with modern .NET, here is one, can provide more.
You can use dependencies that aren't using nullable reference types in projects that use it. You can enable/disable nullable reference types per file, as it only influences static analysis. There's no runtime difference between a non-nullable reference type and a nullable reference type.