Hi! Let me help you with this issue.
Please follow these steps.
Please make sure the mouse is on.
Check the power switch under the mouse.
If it has a battery, try replacing it or charging it.
Look for a blinking light — that usually means it’s in pairing mode.
And then go to Settings → Bluetooth & devices
Click Devices
If you see your mouse listed, but it says “Not connected”:
Click the 3 dots
Choose Remove device
Click Add device
Select Bluetooth
Put the mouse in pairing mode again
Click your mouse when it appears.