Many suggestions...

Try the laptop with a different monitor or even a TV. If that works, then you know that the laptop and HDMI are probably OK. If that doesn't work, then maybe something else below will help.

Try the monitor with a different computer or laptop. If it doesn't work, then there may be an issue with it. (Coincidences happen.)

In the Windows Settings under System > Display, are there two displays listed (one for the laptop and another for the monitor)?
If only one for the laptop, then it would appear Windows does not see or recognize the external monitor. Most laptops have a function key combination to enable external monitors or toggle between using the laptop and monitor...try that and see it shows up. Also, under "Multiple Displays" there is a "Detect other display" button...try that.
If Windows Display settings does show both displays, but is not displaying, you can try the Identify display button or maybe try toggling between the different Extend and Duplicate display settings.

If none of that helps...

Open Device Manager and look for any devices with yellow exclamation marks indicating problems. If there are any (especially related to video cards or displays) then you may have a driver issue. You may need to try uninstalling and re-installing the device and or the drivers/software for it.

If still no-go, verify you have the latest versions of BIOS & firmware updates and drivers/software.

Past that, you may need to ask a tech friend. If there's a local tech store, bring your laptop there and tell them your monitor seems to have died and you want to try your laptop with some of theirs to see if they're compatible...may get some free assistance.

Dual Monitor not working WIN 11