Magento 2: Difficulty in add simple product, product get added as virtual product

This issue is occurs because the simple product you have added it has no weight. you have choosen This item has no weight option from Weight attribute.

Please check Weight attribute of Simple Product. Make sure you selected The item has weight option. You can leave Weight field blank if you dont ' want to add weight. You must need to select option The item has weight.

Clear the cache by runnning cache:clean commmand and check.

Go to admin Products -> Catalog add product from upper right corner there is dropdown click on simple product as show in below image

Add weight greater than 0 and select This item has weight and save product.