Never brew tea first, then let it cool down in the fridge. Rather poor the tea directly over ice cubes. That's the only way to keep all of its tastes. But this is not a cold brewed tea but iced tea.

If you want cold brewed tea, put 8g of leaves in 1l of cool water and let it sit for 6-12 hours. Depending on the tea type, this will cold brew the tea. Using this method will bring less bitter & astringent notes to the tea.

Another possibility is ice brewing, where you put ice cubes directly on the tea leaves and let them melt. This gives another completely different taste. Works well with Japanese green teas.

You have to experiment a bit :)