Slackware ARM [hard float point] installer image and system packages for the Raspberry Pi 4 Model B are available from SARPi Project downloads page: http://sarpi.fatdog.eu/index.php?p=downloads
End-to-end installation instructions and tutorial are also available, should you need them, from the SARPi Project website.
Slackware ARM on the Raspberry Pi 4 Model B
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SARPi Project - Slackware ARM on a Raspberry Pi
http://sarpi.fatdog.nl
SARPi Project - Slackware ARM on a Raspberry Pi
http://sarpi.fatdog.nl