How to get programmatically order data by order id in magento 2?

You can get order data by Order id using below code snippets,

Call function in template file by below way,

The result will be given order data of specific order id.

How to get payment method title of an order in magento 2?

You can get payment method title of order by below code snippets,

How to override magento 2 order/items/renderer/default.phtml?

We can override default.phtml file using below way,
Create sales_order_item_renderers.xml in your module layout folder,
File path will be in your module,
app/code/Rbj/Training/view/frontend/layout/sales_order_item_renderers.xml

Replace Rbj_Training with your actual module name.

Clear Cache and check your file will be overridden.