Please report any issues in the QtTinySA github 'issues' page and not here.
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Uli, this will likely be something missing or the wrong version in you installation.? I don't have Debian but use the derivative Kubuntu 22.04 and 24.04, and Bookworm-based PiOS and it works on all of those.
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The wikis may give you a clue.
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https://github.com/g4ixt/QtTinySA/wiki/Raspberry-Pi-OS12
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Ian