How to remove the stand from my iMac?

+1, the stand cannot be removed. If you wanted a 2023 with a VESA mount, return the model you bought and Apple sells VESA prepared 2023 iMacs. You can find them at, this is the US site so if you are outside the USA go to the iMac Buy page for your country and you will find a link for the VESA versions on that page.:

Buy 24-inch iMac with Built-in VESA Mount Adapter - Apple

You can not remove the stand from the M3 iMac's.

If you want an M3 iMac with a VESA mount, then you must order it that way from Apple.

see > https://www.apple.com/shop/buy-mac/imac-vesa

You can't but you can get an adapter for around £20 ($25) such as the one below.

https://www.allcam.uk/product/imad03-vesa-adapter-for-mounting-imac-m1-to-an-lcd-monitor-arm-stand/

Mal-S wrote:

You can't but you can get an adapter for around £20 ($25) such as the one below.

That is pretty impressive, and it leaves you a handy spot to put your pens!