I am able to successfully boot a Moto G5S+ (and a couple of other phones, just for fun) without using the power button, so I’m hopeful this will work for you.
To start, you’ll need a tool on your computer called ADB. Instructions to set it up are here:
You can ignore the first part about enabling developer options on your phone, and just skip to the part about installing ADB on your computer. Follow the appropriate instructions for your computer (Windows/Mac/Linux) until you have successfully opened the command prompt within the platform-tools folder. If you do a directory of that folder, you’ll see an executable file called fastboot, and you’ll know you’re in the right directory.
Next, use a USB-micro data cable to connect your phone to your computer - and hold the volume-down button as you’ve successfully done when connecting to a charger. Just as when you connected to the charger, you’ll continue to hold the volume-down button until the phone boots into the recovery menu. You can then release the volume-down button…
Now, in the command prompt on your computer, within the platform-tools directory of ADB, type:
and press enter.
This will send a command to the phone to reboot, and it will reboot normally, not into recovery.