The .NET team recently announced support for .slnx, a new, simplified solution file format for the .NET CLI:
Introducing support for SLNX, a new, simpler solution file format in the .NET CLI.

PowerShell currently uses traditional .sln files in its build and development workflow. As .slnx gains traction, adopting it may simplify contributor experience and align PowerShell with modern .NET tooling practices.

Draft changes from automated conversion using dotnet sln migrate: xtqqczze@1d7529a