The Debian packaging of libcsfml is maintained in git, using the
merging workflow described in dgit-maint-merge(7).  There isn't a
patch queue that can be represented as a quilt series.

A detailed breakdown of the changes is available from their canonical
representation - git commits in the packaging repository.  For
example, to see the changes made by the Debian maintainer in the first
upload of upstream version 1.2.3, you could use:

    % git clone https://git.dgit.debian.org/libcsfml
    % cd libcsfml
    % git log --oneline 1.2.3..debian/1.2.3-1 -- . ':!debian'

(If you have dgit, use `dgit clone libcsfml`, rather than plain
`git clone`.)

A single combined diff, containing all the changes, follows.
--- libcsfml-3.0.0~rc3.orig/doc/CMakeLists.txt
+++ libcsfml-3.0.0~rc3/doc/CMakeLists.txt
@@ -28,7 +28,7 @@ configure_file(doxygen.css html/doxygen.
 configure_file(searchOverrides.css html/searchOverrides.css COPYONLY)
 
 # target setup
-add_custom_target(doc ALL
+add_custom_target(doc
                   COMMAND ${CMAKE_COMMAND} -E echo_append "Building API Documentation..."
                   COMMAND Doxygen::doxygen ${CMAKE_CURRENT_BINARY_DIR}/doxyfile
                   COMMAND ${CMAKE_COMMAND} -E echo "Done."
--- libcsfml-3.0.0~rc3.orig/test/CMakeLists.txt
+++ libcsfml-3.0.0~rc3/test/CMakeLists.txt
@@ -2,22 +2,9 @@ include(FetchContent)
 
 set(CATCH_CONFIG_FAST_COMPILE ON CACHE BOOL "")
 set(CATCH_CONFIG_NO_EXPERIMENTAL_STATIC_ANALYSIS_SUPPORT ON CACHE BOOL "")
-FetchContent_Declare(Catch2
-    GIT_REPOSITORY https://github.com/catchorg/Catch2.git
-    GIT_TAG v3.7.0
-    GIT_SHALLOW ON)
-FetchContent_MakeAvailable(Catch2)
+find_package(Catch2 3.7 REQUIRED)
 include(Catch)
 
-# Build Catch2 in C++17 mode to enable C++17 features
-target_compile_features(Catch2 PRIVATE cxx_std_17)
-
-# Ensure that Catch2 sources and headers are not analyzed by any tools
-set_target_properties(Catch2 PROPERTIES COMPILE_OPTIONS "" EXPORT_COMPILE_COMMANDS OFF)
-set_target_properties(Catch2WithMain PROPERTIES EXPORT_COMPILE_COMMANDS OFF)
-get_target_property(CATCH2_INCLUDE_DIRS Catch2 INTERFACE_INCLUDE_DIRECTORIES)
-target_include_directories(Catch2 SYSTEM INTERFACE ${CATCH2_INCLUDE_DIRS})
-
 set(CMAKE_CATCH_DISCOVER_TESTS_DISCOVERY_MODE PRE_TEST)
 
 add_executable(test-csfml-system
