Why not ask them?
https://github.com/linuxserver/docker-ombi/issues
https://discourse.linuxserver.io/
And probably related: https://www.linuxserver.io/blog/a-farewell-to-arm-hf
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We welcome posts that include suggestions for good self-hosted alternatives to popular online services, how they are better, or how they give back control of your data. Also include hints and tips for less technical readers.
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Why not ask them?
https://github.com/linuxserver/docker-ombi/issues
https://discourse.linuxserver.io/
And probably related: https://www.linuxserver.io/blog/a-farewell-to-arm-hf
If your pi is one of the old 32-bit processors, then no- linuxserver no longer supports that isa.