Running SQL Server in fibre mode (lightweight pooling) disables the use of SQL CLR:
Common language runtime (CLR) execution is not supported under lightweight pooling. Disable one of two options: "clr enabled" or "lightweight pooling". Features that rely upon CLR and that do not work properly in fiber mode include the hierarchy data type, replication, and Policy-Based Management.
On the other hand, disabling SQL CLR alone (without enabling lightweight pooling) does not disable the built-in CLR types like
hierarchyid is mentioned above), as shown in How can "HierarchyID" type work when "CLR" is disabled?
Now some new language features rely on the CLR, for example the
FORMAT relies on the presence of the .NET Framework Common Language Runtime (CLR).
Does running SQL Server in fibre mode disable the
FORMAT function and/or using the CLR types?