This thread keeps giving! Okay...I'll play.
I never understood the need for a Garmin. Just mount your smartphone on your stem and use Strava.
My setup uses a Quad Lock for the phone, with an accessory battery bar extension.
Got it on Amazon for less than twenty bucks. Both USB-A and USB-C plugs.
Never got around to buying a shorter cable. Someday will do it. lol
It keeps my phone 100% charged for five hours, with my screen full on the entire ride.
That blue-lit button allows me to turn off the charger, for whatever reason.
My attached integrated-battery headlight can likewise accept a charge or give out a charge.