can i remove the stand of 27 inches IMac 2019?

No, they are permanently attached to the chassis. However if you have not purchased your iMac yet, there are VESA mount versions available directly from Apple. You can find them at:

21.5" version https://www.apple.com/shop/buy-mac/imac-vesa

27" version https://www.apple.com/shop/buy-mac/imac-vesa

If you already bought the iMac and it's less than 2 weeks old, return it ASAP and buy the Vesa mount version.

You can apparently purchase the 27" iMac with a VESA mount but it appears that you cannot customize a standard iMac after the fact. Buy iMac with Built-in VESA Mount Adapter - Apple

Your very welcome.