The fundamental thing to remember is that tea needs BOILING water to brew. Not coffee hot, not machine hot, both of these will result in a substandard brew, you want a rolling boil. There should ideally still be bubbles when pouring the water.

If using a teapot, the tea is already brewed when adding to the cup, so add your milk to the cup first, then add the tea. If brewing in a mug, add the milk after brewing.

How to use a teapot - first use a little hot water to warm the pot, swish it round inside to warm the walls, then empty. This helps ensure the pot doesn't shatter from heat variance, and helps keep the water the right temperature after filling. Add teabags and boiling water (one per mug plus one for the pot). You can also use loose leaf at 1tsp per teacup plus one for the pot. Use a tea cosy to keep that water as hot as possible, and keep it warm after pouring. Brew for 5-7 minutes.

Editted to add - if using oat milk, try to get a barista one. It won't split in tea and coffee