Already fixed in master so can be removed with next release (1.21+)
-------------
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -213,6 +213,10 @@
     $<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/include>
     $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>
 )
+
+set_target_properties(leveldb
+  PROPERTIES VERSION ${PROJECT_VERSION} SOVERSION ${PROJECT_VERSION_MAJOR})
+
 target_compile_definitions(leveldb
   PRIVATE
     # Used by include/export.h when building shared libraries.