The integration package is needed even when running in legacy mode. This is what installs index templates, ingest pipelines, and ILM policies in Elasticsearch.
It should be enough to add this to your kibana.yml config file:
xpack.fleet.packages:
- name: apm
Then when you (re)start Kibana, it should install the integration package. The APM integration package is bundled with Kibana, hence you don't need to run a separate Elastic Package Registry container, etc.