Leex/Heex

example.ex

defmodule SearchLive do
.....STUFF

  def render(assigns) do
    template_extension = if FeatureFlag.enabled?(), do: ".heex", else: ".leex"
    
    # I can't remember the exact API to directly render a template, but it's something like this:
    Phoenix.View.render("search_live.html.#{template_extension}", assigns) 
  end 
end

THEN:

(search_live.html.heex) *just waving my hands here but something like this, assuming `render_ad_card` is a ~H-based render function*
<InventoryAdCard.render_ad_card {@assigns} />

(search_live.html.leex) 
<%= live_component InventoryAdCard, ...assigns %>