async-simple provides CMake targets:

find_package(async_simple CONFIG REQUIRED)
target_link_libraries(main PRIVATE async_simple::async_simple_static)
# Or you can use header-only version(async_simple::uthread is not allowed to use in this version)
target_link_libraries(main PRIVATE async_simple::async_simple_header_only)
# Or you can also use dynamic linkage:
target_link_libraries(main PRIVATE async_simple::async_simple)