Use github issues, as usual. It's likely that any problems come from versions of strace we haven't tested against, so be sure to provide that version. It's unexpected that this works anywhere but on Linux.
New features are of course welcome. Tests, linting, doc builds, and coverage diffs will automatically be run on new PRs, so just go ahead and create one if you think you have something good to add.
flametrace doesn't depend on much, you should be able to clone it, run pip install -e . into a virtualenv, and start editing and testing by running flametrace.
The easiest way to get a development environment is to clone it in a VS Code devcontainer. There is a good default environment set up in the repository, which you can get by cloning straight into a devcontainer.
You can run the tests with unittest, or with tox -e py39 (or your favorite modern Python 3). You can run tests with coverage with tox -e coverage (the default devcontainer setup will show coverage in the gutter).
We use flake8 with tox -e flake8.
You can build the docs with tox -e docs. In the devcontainer, Ctrl-Shift-B will build the docs and run an HTTP server so you can view them.