The solar cell only extends the battery life, you still need to charge it (about once a month). There are several other Fenix 6 models too.
Garmin announces Fenix 6 series: Solar power, bigger displays, and grade-adjusted pacing
Garmin Fenix 6 Pro Solar review: the solar-powered super watch, Smartwatches
Garmin fenix 6, 6 Pro, and 6X Pro Solar Announced! – DesFit
Garmin fenix® 6X - Pro Solar Edition
The fenix 6X Pro Solar multisport GPS watch puts no limits on how far you can go. Its unique power-replenishing feature extends battery life, so you'll have more on-wrist time to enjoy the watch's color mapping, music streaming and other advances. Other highlights include enhanced wrist heart rate, and smart notifications.
Garmin Fenix 6X Pro Solar Gray Black
Garmin Fenix 6 Pro Solar Edition GPS smartwatch review
Garmin fenix 6X Pro Solar, Premium Multisport GPS Watch with Solar Charging Capabilities, Features Mapping, Music, Grade-Adjusted Pace Guidance and Pulse Ox Sensors, Dark Gray with Black Band : Electronics
Garmin fenix 6X Pro Solar Edition GPS Smartwatch
Garmin fenix 6X Pro Solar Multisport GPS Watch
Garmin Fenix 6 Series In-Depth Review