Your ROOT_URL in app.ini is https://git.cloudchain.link/ but you are visiting https://dash.bss.nz/open-source-mirrors/jellyfin/blame/commit/ec3237ba55a6c0c6e7a31e2aaa5fbf77c9978ac7/deployment/Dockerfile.ubuntu.amd64
You should set ROOT_URL correctly, otherwise the web may not work correctly.
FROM ubuntu:bionic
# Docker build arguments
ARG SOURCE_DIR = /jellyfin
ARG ARTIFACT_DIR = /dist
ARG SDK_VERSION = 5 .0
# Docker run environment
ENV SOURCE_DIR = /jellyfin
ENV ARTIFACT_DIR = /dist
ENV DEB_BUILD_OPTIONS = noddebs
ENV ARCH = amd64
ENV IS_DOCKER = YES
# Prepare Debian build environment
RUN apt-get update \
&& apt-get install -y apt-transport-https debhelper gnupg wget devscripts mmv libc6-dev libcurl4-openssl-dev libfontconfig1-dev libfreetype6-dev libssl-dev libssl1.1 liblttng-ust0
# Install dotnet repository
# https://dotnet.microsoft.com/download/linux-package-manager/debian9/sdk-current
RUN wget https://download.visualstudio.microsoft.com/download/pr/a2052604-de46-4cd4-8256-9bc222537d32/a798771950904eaf91c0c37c58f516e1/dotnet-sdk-5.0.103-linux-x64.tar.gz -O dotnet-sdk.tar.gz \
&& mkdir -p dotnet-sdk \
&& tar -xzf dotnet-sdk.tar.gz -C dotnet-sdk \
&& ln -s $( pwd ) /dotnet-sdk/dotnet /usr/bin/dotnet
# Link to build script
RUN ln -sf ${ SOURCE_DIR } /deployment/build.ubuntu.amd64 /build.sh
VOLUME ${SOURCE_DIR}/
VOLUME ${ARTIFACT_DIR}/
ENTRYPOINT [ "/build.sh" ]