Generally before start deploying container check on
Docker Hub (when Docker registry is used) if specific tag for container image supports your device CPU architecture which is ARM (32-bit) by looking at device
product page, image should have builds for
linux/arm/v6 or
linux/arm/v7 architectures, in this case latest tag (latest tag is fetched if not specified for remote image) in
unifi-controller tags have builds only for
linux/amd64 (x86-64) and
linux/arm64 (ARM64) and that is reason of this error, your device architecture is not supported for this image tag.
Some container images can have different tag for some architecture, like older version tag when latest build is made for arhitecture supported by your device, you can try to filter tags by
arm or
arm32 keywords to find it, example
https://hub.docker.com/r/linuxserver/un ... name=arm32 and you can see there is
arm32v7-7.3.83 latest tag with supported arch (there is also arm32v7-latest and arm32v7-mongoless tags but with wrong arch), if that older version suits you, you can try to add container with remote image
linuxserver/unifi-controller:arm32v7-7.3.83
.