If you are looking to engrave a material that is over 2" think you need to use the Boss laser, not the Glowforge. The table in the Boss laser drops down to allow thicker materials to be engraved, the Glowforge does not have this feature.

On the Glowforge the maximum thickness of a item to engrave is .5".  If the item is over .5" but under 2" it is possible to engrave it without the crumb tray.

There is a very helpful guide for doing the calculations needed at https://caughtbydesign.com/how-to-use-your-glowforge-without-the-crumb-tray/

In the calculations below, the item is .97" thick.  Substitute the actual thickness of the item you have in place of the .97"