On 99% it’s microswitch. U can replace it . Find this on your region https://www.amazon.co.uk/Mouse-Switch-Microswitches-Logitech-Anywhere/dp/B00T1CWZSI U have help here on this website Logitech Anywhere Mouse MX Micro Switch Replacement
It’s hard to help you. I was trying flashing via SP flash tool. Sometimes o found right scatter file some times don’t. Try if adb or fastboot find phone or this webistes https://forum.xda-developers.com/?query=LG%20G3%20Stylus https://forum.xda-developers.com/android/general/unbrick-lg-model-download-recovery-t3060184
