With VS 2022 v17.14 the slnx format is no longer in preview.
I made a quick test:
When I open NCrunch I must re-enable it because the NCrunch file name is now different.
Old file name (with sln)
Solution.v3.ncrunchsolutionNew file name (with slnx)
Solution.slnx.v3.ncrunchsolutionIt is not even a problem cause renaming the file makes everything work like before, but I find it a little inconsistent to strip the extension in once case but not the other.
I think stripping the slnx from the name would make the user experience way better