in some cases with EFI installs the calamares installer fails near the end of the installation process - this is a now known bug and forwarded to upstream.
Trigger for that behaviour is the existence of /EFI/Boot in the EFI partition. The bug could be considered as "not so nice" - but most installations will still work without problems. Sounds nuts - but isn't - the bug occours when the system is trying to write the fallback EFI loader - while the primary EFI loader is written and will work - allso other things the installer should do are fully finished, except for the fallback, unmount and the final screen. One can ignore this bug or in the rare cases if the fallback loader is needed because of crappy vendor EFI defaults reboot the machine, rename or remove the fallback folder and install again.
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https://github.com/calamares/calamares/issues/692
