@lochan: Yep, no Python, no Font Overrides menu

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The install script requires 325MB of free space, so that's probably it

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You can check MRPI's logs (in extension/MRInstaller/log) to confirm.
(If you're *really* short on space and you *already* had Python installed, you can manually remove the python & python3 folders first, because they should really take around 150MB each, so that 325MB check is already cutting it pretty close).