I know your post is old, but I've been struggling too with connecting Flic 2 and Home Assistant. Using Flicd addon didn't give a stable integration, but this is a workaround I've found was quite stable. Works only with a Flic Hub and Apple Homekit running!
In Home Assistant, set up an input boolean for single, double and hold for each Flic button. That's three input booleans for each button.
Then expose Home Assistant to Homekit via the Homekit integration. You should now be able to control Home Assistant entities in Homekit, including your new input booleans.
In the Flic app, set up your Flic button to run through Homekit
In Homekit app, set up the button to turn on the input booleans corresponding to single, double and hold press.
You can now create automations in Home Assistant, that fires when the states for your input booleans turn on. Also make an automation that turns off the input booleans again.