Try #700:

.jenkins/cscs/env-gcc-cuda-11.sh

@@ -4,7 +4,8 @@
 # Distributed under the Boost Software License, Version 1.0. (See accompanying
 # file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
 
-cxx_std="17"
+cxx_std="20"
+cuda_std="17"
 gcc_version="9.3.0"
 boost_version="1.75.0"
 hwloc_version="2.0.3"
@@ -15,6 +16,7 @@ spack_arch="cray-cnl7-haswell"
 spack_spec="pika@main arch=${spack_arch} %${spack_compiler} +cuda malloc=system cxxstd=${cxx_std} ^boost@${boost_version} ^hwloc@${hwloc_version} ^cuda@${cuda_version}"
 
 configure_extra_options+=" -DPIKA_WITH_CXX_STANDARD=${cxx_std}"
+configure_extra_options+=" -DCMAKE_CUDA_STANDARD=${cuda_std}"
 configure_extra_options+=" -DPIKA_WITH_MALLOC=system"
 configure_extra_options+=" -DPIKA_WITH_CUDA=ON"
 configure_extra_options+=" -DPIKA_WITH_EXAMPLES_OPENMP=ON"

cmake/pika_setup_cuda.cmake

@@ -28,14 +28,15 @@ if(PIKA_WITH_CUDA AND NOT TARGET pika_internal::cuda)
     # support
     if(NOT PIKA_FIND_PACKAGE)
       if(DEFINED CMAKE_CUDA_STANDARD AND NOT CMAKE_CUDA_STANDARD STREQUAL
-                                         PIKA_WITH_CXX_STANDARD
+                                         CMAKE_CXX_STANDARD
       )
-        pika_error(
-          "You've set CMAKE_CUDA_STANDARD to ${CMAKE_CUDA_STANDARD} and PIKA_WITH_CXX_STANDARD to ${PIKA_WITH_CXX_STANDARD}. Please unset CMAKE_CUDA_STANDARD."
+        pika_info(
+          "You've set PIKA_WITH_CXX_STANDARD to ${PIKA_WITH_CXX_STANDARD} and CMAKE_CUDA_STANDARD to ${CMAKE_CUDA_STANDARD}."
         )
+      else()
+        set(CMAKE_CUDA_STANDARD ${PIKA_WITH_CXX_STANDARD})
       endif()
 
-      set(CMAKE_CUDA_STANDARD ${PIKA_WITH_CXX_STANDARD})
     endif()
 
     set(CMAKE_CUDA_STANDARD_REQUIRED ON)
@@ -64,7 +65,7 @@ if(PIKA_WITH_CUDA AND NOT TARGET pika_internal::cuda)
     endif()
     # Flag not working for CLANG CUDA
     target_compile_features(
-      pika_internal::cuda INTERFACE cuda_std_${PIKA_WITH_CXX_STANDARD}
+      pika_internal::cuda INTERFACE cuda_std_${CMAKE_CUDA_STANDARD}
     )
     set_target_properties(
       pika_internal::cuda PROPERTIES INTERFACE_POSITION_INDEPENDENT_CODE ON