There is no addon store when running the home assistant container version. See this thread.
Technically, the addons are themselves docker containers that are managed by the home assistant supervisor. What addons did you want to use? You generally can install the equivalent full version of the addon in docker. For example, you already installed portainer so wouldn’t need the portainer addon. I have zwavejs2mqtt, Zigbee2mqtt, and node red all installed independently through docker, but they still work with Home Assistant container. I can post install instructions on one you would need if I’m familiar with them.
I posted about reasons why in the thread below.
The main reason is you can install other software on the machine besides homeassistant. With hassos, you can only install addons. Other options include “supervised”, which has a lot of requirements (if using raspberry OS you already aren’t meeting them), and a VM, which isn’t as efficient at managing resources as docker.
If you’re not going to use the rpi for anything beside home assistant or the addons though, best to just use homeassistant os as detailed here, with full access to the addon store.