Fenix 6 x pro Watch just stopped working, won’t charge, just gets super hot.

This sounds like a hardware defect, possibly the Li-Ion battery. You'll need to contact Garmin to get it inspected and fixed.

As for the four years lifespan, that is consistent with how long Li-Ion batteries last on average. This is an issue with all devices that use them, from smartwatches to Apple iPhones. 

Thank you so much for replying, I finally found my serial number and will go through the channels to send it off and see how much I’m up for. Shame really as it works out to be around $3-400 a year

Bylo Selhi said:

As for the four years lifespan, that is consistent with how long Li-Ion batteries last on average. This is an issue with all devices that use them, from smartwatches to Apple iPhones. 

That is not correct. The service life of a Li Ion battery depends very much on how it is treated.
The service life is therefore not measured in years, but in charging cycles. If you adhere to the 20-80% charging technique, you will be able to more than double the service life of a LiIon battery.

I said "on average." There is variance among samples.While 4 years may be at the low end of average it's hardly an outlier. 

Plus we don't know if the battery was indeed kept between 20% and 80%. It's hard to do that with a smartwatch because there's no automatic way to stop charging at 80% nor is it always possible to recharge it when it gets to 20%. Letting a Li-Ion battery discharge to 0% and/or letting it sit on a charger at 100% accelerates the deterioration of a Li-Ion battery, 

Considering your watch was purchased in 2020, are you still within the warranty period, and have you contacted Garmin support to discuss the issue before considering sending it to Garmin Australia for repair?