pkg-config can not resolve dependencies

What version of protobuf and what language are you using?
33.0
Language: C++

What operating system (Linux, Windows, ...) and version?
Linux (Ubunut)

What runtime / compiler are you using (e.g., python version or gcc version)
clang 21

What did you do?

1. build from source using CMake and install to any DIR
2. set PKG_CONFIG_PATH to the DIR/lib/pkgconfig
3. execute pkg-config protobuf --cflags or pkgconf protobuf --cflags
4. Additional step is to execute pkgconf protobuf --digraph

What did you expect to see
The output should be there within seconds
The dependencies graphs should have a sane size

What did you see instead?
pkg-config/pkgconf got stuck for minutes (I've been waiting for around 15)
The graph is insanely large (>2 millions nodes)

I'm honestly not an expert with any of pkg-config or pkgconf, but to me it looks like some kind of cyclic dependencies somewhere in CMake files

Start by reproducing the source build and install with CMake, then run the reported pkg-config and pkgconf commands with PKG_CONFIG_PATH set to the installed lib/pkgconfig directory. Inspect the generated package metadata and dependency graph to identify why resolution expands to millions of nodes. Done means the commands complete promptly and the graph has a sane size.