Backspace and Delete key not work for me.
And how about searching in inventory and hotbar too, pls?
(1.16.5)

Do you have any other mods installed? And which keyboard layout are you using? On my end backspace works, so I'm wondering if maybe there's an incompatibility I'm not aware of. Let me know and I'll test it out.

As for searching in inventory and hotbar, my main barrier at the moment is just the design of where to place the search bar.

As it is. I thought to search the inventory & hotbar only in chest gui.

My privat modpack has 100+ mods.
I'm looking for a chest/backpack/inventory search mod.
With Quark search and Quicksearchmod I can edit text well.
But they have other problems...

So the problem with the edit keys is this: I use Backspace, Delete, Left and Right keys as hotkeys for other mods, and your mod doesn't see them when pressed, even though it has focus for editing.
Is there anything you can do about it? For example, backspace is used by default in JEI.
(sorry for my English)

No worries! Unfortunately if that is the issue it is caused by the other mods canceling the key press event, so it never reaches my mod's handlers. You would have to change the hotkeys for the other mods, as far as I'm aware there's no way on my end to fix that.