To answer your question directly first, yeah, the Fenix 5 is essentially end of life. But, EOL is all relative. Support-wise, you can call Garmin with an issue and they’ll happily work the issue with you. But it’s not getting new features. It might get the errant bug fix if something major happens (latest update as you noted was 25.00, which was Feb 2022).
For context, the Fenix 5 is basically 6 years old (announced first week of January 2017).
Fenix 5: Early January 2017
Fenix 5 Plus: June 2018
Fenix 6: Late August 2019
Fenix 6 Solar lineup: July 2020 (the Fenix 6X did have Solar at launch, but not the others, this added it to all units)
Fenix 7: January 2022
Roughly speaking, Fenix series has been on a 14-18 month refresh cycle, till COVID. That obviously dorked that up. I suspect Gamrin would prefer to get bak to that 14-18 month refresh cycle, because that simply means more money for them.
In terms of updates for previous gen units, the Outdoor team has pushed back a number of Fenix 7 (and some Forerunner 955 features) to the Fenix 6, at least initial launch ones. Then from summer it’s gotten slimmer, though it did get HRV updates. Unfortunately, in Garmin’s eyes, it’s largely a 'What have you done for me lately" type of mentaility for firmware updates. The Edge team is far better (and inversely, the Venu/Vivo team worse).
For context, while Apple pushes update back about 4ish years (Series 4 watches got updates this time around, 4 years older), others like Polar don’t push meaningful updates to previous gen units. Suunto generally has over the past year pushed to previous gen devices, which is great. COROS kinda splits the difference, in that some devices have gotten it while others haven’t. I think in their case that’s more tied to them growing up real fast, and their previous gen (which was 1st gen in many cases) lineup simply didn’t have the hardware potential/space they needed.