After updating to 23h2, the non-numpad Insert and Del keys stopped working

The Insert key now does not do anything, the Del key produces "+" sign. All other keys (including the PrtSc key located between them) work as expected.

This appeared after update from 21h2 to 23h2.

No information filled in there to give a clue to the issue. There can be problems when skipping a Version upgrade and sometimes with Build updates to that.
Windows Key + R, type winver, post the line about Version. Current:

I have the same build number as yours.

Sounds like a keyboard issue, do you have a spare you can try?
If it isn’t, seems to be some odd goings on after update KB5035853

A while ago, I was having trouble with keys that were doing things they weren't meant to, pressing the backspace was opening settings, couldn’t type text on a notepad file, just odd behaviour. It may of been caused by a game launcher I have or my corsair keyboard software but I never worked it out.
I pressed the Win key a few times and for some reason it appeared to have solved it. But that could of been a fluke coincidence. Assuming you have rebooted since this happened?

Sorry, I see you have a Dell, I assume it is a Laptop. Still, a USB keyboard plugged in could eliminate the possibility that your Dell laptop keyboard is malfunctioning.

Is it possible that on your keyboard you need to press a key such as "Fn" along with those keys? That is common practice on many laptops. There may also be a setting that allows you to toggle which function is enabled by default on those keys.

Put another way, it is typical for many laptop keyboards to have a series of keys that can perform more than one function. Many systems allow you to toggle which function those keys perform by default.

As an example, I am typing this message on an ASUS laptop. Most of my function keys serve two purposes. For example, my F1 key also has the ability to mute audio if I press Fn + F1. Likewise, my Delete key also serves as the INS key if I press it along with Fn.

Anixx said:

The Insert key now does not do anything, the Del key produces "+" sign. All other keys (including the PrtSc key located between them) work as expected.

Click to expand...

I'm running a HP laptop with the latest 23H2 update (KB5035853). My number pad keys seem to be operating correctly. In the non-number mode, the "ins" key, on my laptop, also appears to do nothing. In the number mode, the "ins" key inserts a "0". The "del" key, when enable, does a forward delete. I use the "backspace" for a reverse delete. When disabled, it types a ".".

I don't use the number pad, except for the "home" and "end", that often, so I don't remember if it worked differently before. My keyboard is always in the "insert" mode so I don't find the "ins" key very useful. I just locate my cursor in the text, or select the text I want to replace, and start typing. Existing text then moves out of the way. If I need to open blank space, I just use the space bar.

On my keyboard, the functions keys require the "fn" to operate as a function key. Without the "fn" key they control the screen brightness, audio off/up/down and video pause/fwd/rev. The "prt scr" key works normally, but also doubles as a "ins" key, with the "fn" key. However, it also does nothing.