diff --git a/CMakeLists.txt b/CMakeLists.txt
index f1706848..7a4dc80f 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,7 +1,7 @@
 cmake_minimum_required(VERSION 3.19)
 
 project(opencmw-cpp CXX)
-set(CMAKE_CXX_STANDARD 20)
+set(CMAKE_CXX_STANDARD 23)
 
 # include(cmake/StandardProjectSettings.cmake)
 include(cmake/PreventInSourceBuilds.cmake)
@@ -126,7 +126,10 @@ if(OPENCMW_ENABLE_TESTING)
   if(OPENCMW_ENABLE_COVERAGE)
     if(UNIX
        AND NOT APPLE
-       AND NOT CMAKE_CXX_COMPILER_ID MATCHES ".*Clang"
+       AND NOT
+           CMAKE_CXX_COMPILER_ID
+           MATCHES
+           ".*Clang"
        AND NOT EMSCRIPTEN) # Linux
       message("Coverage reporting enabled")
       include(cmake/CodeCoverage.cmake) # https://github.com/bilke/cmake-modules/blob/master/CodeCoverage.cmake #
diff --git a/src/core/include/URI.hpp b/src/core/include/URI.hpp
index 64f7c760..7bc2373b 100644
--- a/src/core/include/URI.hpp
+++ b/src/core/include/URI.hpp
@@ -1,7 +1,7 @@
 #ifndef OPENCMW_CPP_URI_HPP
 #define OPENCMW_CPP_URI_HPP
 #include <algorithm>
-#include <fmt/format.h>
+#include <cassert>
 #include <iomanip>
 #include <ios>
 #include <optional>
@@ -10,7 +10,8 @@
 #include <string_view>
 #include <unordered_map>
 
-#include <cassert>
+#include <fmt/format.h>
+#include <fmt/std.h>
 
 namespace opencmw {
 
@@ -476,25 +477,6 @@ struct std::hash<opencmw::URI<check>> {
 
 // fmt::format and std::ostream helper output
 
-// fmt::format and std::ostream helper output for std::optional
-template<typename T> // TODO: move to utils class
-struct fmt::formatter<std::optional<T>> {
-    template<typename ParseContext>
-    constexpr auto parse(ParseContext &ctx) {
-        return ctx.begin(); // not (yet) implemented
-    }
-
-    template<typename FormatContext>
-    auto format(std::optional<T> const &v, FormatContext &ctx) const {
-        return v ? fmt::format_to(ctx.out(), "'{}'", v.value()) : fmt::format_to(ctx.out(), "{{}}");
-    }
-};
-
-template<typename T>
-inline std::ostream &operator<<(std::ostream &os, const std::optional<T> &v) {
-    return os << fmt::format("{}", v);
-}
-
 template<opencmw::uri_check check>
 struct fmt::formatter<opencmw::URI<check>> {
     template<typename ParseContext>
diff --git a/src/core/include/opencmw.hpp b/src/core/include/opencmw.hpp
index 9bf32298..3185a89e 100644
--- a/src/core/include/opencmw.hpp
+++ b/src/core/include/opencmw.hpp
@@ -44,8 +44,6 @@ constexpr bool always_false = false;
 using units::basic_fixed_string;
 using units::is_same_v;
 
-constexpr auto &unmove(auto &&t) { return t; } // opposite of std::move(...)
-
 template<typename R, typename Fn, typename... FnArgs>
 concept invocable_r = std::is_invocable_r_v<R, Fn, FnArgs...>;
 
diff --git a/src/core/test/00_opencmw_basic_tests.cpp b/src/core/test/00_opencmw_basic_tests.cpp
index 4ac0d58e..19f7e3d6 100644
--- a/src/core/test/00_opencmw_basic_tests.cpp
+++ b/src/core/test/00_opencmw_basic_tests.cpp
@@ -20,10 +20,6 @@ static_assert(no_fwd_wrapper(0) == 1, "r-value non-forwarding -> converted to lv
 static_assert(fwd_wrapper_verbose(0) == 2, "r-value forwarding");
 static_assert(fwd_wrapper(0) == 2, "r-value forwarding");
 
-/**** unmove(..) tests ***/
-static_assert(fwd_wrapper(unmove(lvalue)) == 1, "l-value -> l-value forwarding (copy)");
-static_assert(fwd_wrapper(unmove(0)) == 1, "r-value -> lvalue forwarding (copy)");
-
 /**** power 2 and bit-magic tests ***/
 static_assert(isPower2(1024U));
 static_assert(is_power2_v<1024U>);
diff --git a/src/core/test/URI_tests.cpp b/src/core/test/URI_tests.cpp
index 46cd46d6..22008a52 100644
--- a/src/core/test/URI_tests.cpp
+++ b/src/core/test/URI_tests.cpp
@@ -268,9 +268,6 @@ TEST_CASE("helper methods", "[URI]") {
     dummyStream << fmt::format("test std::optional fmt::print: '{}'\n", optional);
     REQUIRE(dummyStream.str().size() != 0);
     resetStream();
-    dummyStream << "std::cout std::optional print: " << optional << std::endl;
-    REQUIRE(dummyStream.str().size() != 0);
-    resetStream();
 }
 
 TEST_CASE("lifetime", "[URI]") {
diff --git a/src/serialiser/test/IoSerialiserYaS_tests.cpp b/src/serialiser/test/IoSerialiserYaS_tests.cpp
index dc234e82..36b8ca4e 100644
--- a/src/serialiser/test/IoSerialiserYaS_tests.cpp
+++ b/src/serialiser/test/IoSerialiserYaS_tests.cpp
@@ -447,8 +447,10 @@ TEST_CASE("IoSerialiser basic syntax", "[IoSerialiser]") {
         REQUIRE(opencmw::is_annotated<decltype(data.value)> == true);
         std::cout << fmt::format("buffer size (before): {} bytes\n", buffer.size());
 
-        opencmw::FieldHeaderWriter<opencmw::YaS>::template put<true>(buffer, unmove(FieldDescriptionShort{ .fieldName = "fieldNameA" }), 43.0);
-        opencmw::FieldHeaderWriter<opencmw::YaS>::template put<true>(buffer, unmove(FieldDescriptionShort{ .fieldName = "fieldNameB" }), data.value.value());
+        auto fieldA = FieldDescriptionShort{ .fieldName = "fieldNameA" };
+        opencmw::FieldHeaderWriter<opencmw::YaS>::template put<true>(buffer, fieldA, 43.0);
+        auto fieldB = FieldDescriptionShort{ .fieldName = "fieldNameB" };
+        opencmw::FieldHeaderWriter<opencmw::YaS>::template put<true>(buffer, fieldB, data.value.value());
         std::cout << fmt::format("buffer size (after): {} bytes\n", buffer.size());
     }
     REQUIRE(opencmw::debug::dealloc == opencmw::debug::alloc); // a memory leak occurred
diff --git a/src/zmq/include/zmq/ZmqUtils.hpp b/src/zmq/include/zmq/ZmqUtils.hpp
index d48724fb..209bb369 100644
--- a/src/zmq/include/zmq/ZmqUtils.hpp
+++ b/src/zmq/include/zmq/ZmqUtils.hpp
@@ -14,13 +14,13 @@
 #include <string>
 #include <type_traits>
 
-#ifdef __clang__ // TODO: replace (source_location is part of C++20 but still "experimental" for clang
+#ifdef __cpp_lib_source_location
+#include <source_location>
+#else
 #include <experimental/source_location>
 namespace std {
 typedef std::experimental::source_location source_location;
 }
-#else
-#include <source_location>
 #endif
 
 #ifndef ENABLE_RESULT_CHECKS