I bought the "closed" version, since I'm not a programmer myself and rely on community efforts. So unfortunately I can't provide you with an answer!

Edit: I don't think Infinitime is Linux based, but it is open source: https://infinitime.io/

I'm sure it'll charge from the dim light of my screens just fine /s

Hardware is generally great. Software is the sucky part. And I didn't say device stops working, but Garmin stops providing support for it, as in no software updates or bug fixes. What you buy is what you get. Perhaps first half a year you might get a fix or two if there are serious enough issues. But that's about it. It might be different since Fenix is their premium line, but with my Forerunner it was as I describe.

It's not that device stops working, but they refuse to provide updates. I have Forerunner 220, which was released at about time when Android watches were starting to be a thing. Unfortunately for me, I ran into many issues with the device, where device would freeze mid run and similar issues. I even had watch create corrupted activity file which would cause whole software to crash and restart if you tried to go into activity listing on it. I contacted Garmin, even documented all the issues, provided file system dump, etc. Garmin ignored the bug report and told me to do factory reset. Basically universal solution to them.

Then when Android started pushing features like bluetooth control from watches, Garmin dropped support for 220, and released 235, which was same hardware and slightly updated software. Forerunner 220 never got a software update again after that.

I even went so far to create my own open source tool for synchronization and activity tracking. Garmin wanted 5000$ single time payment for API access, which I was not going to give them. They are ass-backwards company when it comes to software and it shows. Even got some of their developers contact me privately to help but under a promise I won't reveal who they are in fear of retaliation. So no thanks, Garmin never again.