LZ4 is part of our superbuild. It provides a lz4Tagets.cmake file in MITK-superbuild/ep/lib/cmake/lz4. Checked this file on Windows, Ubuntu 20.04 and Ubuntu 22.04. This is the relevant snippet:

# Create imported target LZ4::lz4_shared
add_library(LZ4::lz4_shared SHARED IMPORTED)

set_target_properties(LZ4::lz4_shared PROPERTIES
  INTERFACE_INCLUDE_DIRECTORIES "${_IMPORT_PREFIX}/include"
)

On Ubuntu 22.04, the line that sets the INTERFACE_INCLUDE_DIRECTORIES target property is simply missing. Adding it manually resolves the issue.

But why is it missing on Ubuntu 22.04 and only recently???

To even increase confusion: Same build client, nightly build works just fine.