repro

RUSTFLAGS="-L libs" maturin build
RUSTFLAGS="-L libs" maturin build

also works without RUSTFLAGS, moving the so to /usr/bin.

Logs

maturin build --release

🖨  Copied external shared libraries to package unity-scene-repacker.libs directory:
    /usr/lib/libTypeTreeGeneratorAPI.so
📦 Built wheel to /home/jakob/.cache/rust/wheels/unity_scene_repacker-2.2.2-py3-none-manylinux_2_39_x86_64.whl

unzip -l /home/jakob/.cache/rust/wheels/unity_scene_repacker-2.2.2-py3-none-manylinux_2_39_x86_64.whl

Archive:  /home/jakob/.cache/rust/wheels/unity_scene_repacker-2.2.2-py3-none-manylinux_2_39_x86_64.whl
  Length      Date    Time    Name
---------  ---------- -----   ----
      194  2025-07-14 10:16   unity_scene_repacker-2.2.2.dist-info/METADATA
      105  2025-07-14 10:16   unity_scene_repacker-2.2.2.dist-info/WHEEL
     1073  2025-07-14 10:16   unity_scene_repacker-2.2.2.dist-info/licenses/LICENSE.md
  4023000  2025-07-14 10:16   unity_scene_repacker-2.2.2.data/scripts/unity-scene-repacker
  3632025  2025-07-14 10:16   unity-scene-repacker.libs/libTypeTreeGeneratorAPI-849c9bc2.so
      599  2025-07-14 10:16   unity_scene_repacker-2.2.2.dist-info/RECORD
---------                     -------
  7656996                     6 files

Then, without changing anything:

maturin build --release
💥 maturin failed
  Caused by: Cannot repair wheel, because required library libTypeTreeGeneratorAPI-849c9bc2.so could not be located.

with these logs

2025-07-14T10:21:37.757579Z  INFO into_build_context: maturin::build_options: close time.busy=762ns time.idle=1.79µs
2025-07-14T10:21:37.757613Z DEBUG maturin::project_layout: Found pyproject.toml in working directory at "/home/jakob/dev/unity/unity-scene-repacker/pyproject.toml"
2025-07-14T10:21:37.757743Z DEBUG maturin::project_layout: Using cargo manifest path from pyproject.toml "cli/Cargo.toml"
2025-07-14T10:21:37.757816Z DEBUG resolve_cargo_metadata: maturin::project_layout: Resolving cargo metadata from "/home/jakob/dev/unity/unity-scene-repacker/cli/Cargo.toml"
2025-07-14T10:21:37.825994Z  INFO resolve_cargo_metadata: maturin::project_layout: close time.busy=68.2ms time.idle=801ns
📦 Including license file `LICENSE.md`
2025-07-14T10:21:37.826281Z DEBUG maturin::project_layout: Project layout resolved project_root=/home/jakob/dev/unity/unity-scene-repacker python_dir=/home/jakob/dev/unity/unity-scene-repacker rust_module=/home/jakob/dev/unity/unity-scene-repacker/unity-scene-repacker python_module=Some("/home/jakob/dev/unity/unity-scene-repacker/unity-scene-repacker") extension_name=unity-scene-repacker module_name=unity-scene-repacker
🔗 Found bin bindings
2025-07-14T10:21:37.826337Z DEBUG maturin::build_options: Resolved bridge model: Bin(None)
📡 Using build options bindings from pyproject.toml
2025-07-14T10:21:37.862349Z DEBUG build_wheels: maturin::compile: Running env -u CARGO "cargo" "rustc" "--message-format" "json-render-diagnostics" "--manifest-path" "/home/jakob/dev/unity/unity-scene-repacker/cli/Cargo.toml" "--release" "--bin" "unity-scene-repacker"
    Finished `release` profile [optimized] target(s) in 0.03s
2025-07-14T10:21:37.960068Z DEBUG build_wheels: maturin::module_writer: Adding unity_scene_repacker-2.2.2.dist-info/METADATA
2025-07-14T10:21:37.960134Z DEBUG build_wheels: maturin::module_writer: Adding unity_scene_repacker-2.2.2.dist-info/WHEEL
2025-07-14T10:21:37.960178Z DEBUG build_wheels: maturin::module_writer: Adding unity_scene_repacker-2.2.2.dist-info/licenses/LICENSE.md from /home/jakob/dev/unity/unity-scene-repacker/LICENSE.md
2025-07-14T10:21:37.960476Z DEBUG build_wheels: maturin::module_writer: Adding unity_scene_repacker-2.2.2.data/scripts/unity-scene-repacker from /home/jakob/.cache/rust/release/unity-scene-repacker
2025-07-14T10:21:38.119294Z  INFO build_wheels: maturin::build_context: close time.busy=257ms time.idle=1.90µs