This is already committed in kde overlay for testing (e.g. via eclass-
overrides).

Bug: https://bugs.gentoo.org/920846
Signed-off-by: Andreas Sturmlechner <asturm@gentoo.org>
---
 eclass/cmake.eclass | 1 +
 1 file changed, 1 insertion(+)

diff --git a/eclass/cmake.eclass b/eclass/cmake.eclass
index 41aebeee53..c29dcfe413 100644
--- a/eclass/cmake.eclass
+++ b/eclass/cmake.eclass
@@ -458,6 +458,7 @@ cmake_src_configure() {
 		set(CMAKE_INSTALL_DOCDIR "${EPREFIX}/usr/share/doc/${PF}" 
CACHE PATH "")
 		set(BUILD_SHARED_LIBS ON CACHE BOOL "")
 		set(Python3_FIND_UNVERSIONED_NAMES FIRST CACHE STRING "")
+		set(FETCHCONTENT_FULLY_DISCONNECTED ON CACHE BOOL "")
 	_EOF_
 
 	if [[ -n ${_ECM_ECLASS} ]]; then
-- 
2.43.0