A long-sleeved T-shirt fabric (see photo). I want to know the name of this cloth and where I can buy it.

Look at the photo, it should be knitted beaded mesh. This kind of fabric is very common and is generally used for T-shirts and POLO shirts.

I saw the big picture, which is not quite the same as the beaded net. It should be knitted waffles, which are also called mittens in some places. The plaid of this knitted fabric is large and small, even rectangular. Your grid should be very small, so at first glance it looks like a beaded net.