openwrt uses linux kernel that is very near latest (LTS) release. they kinda have to do this for support added for new devices and new wifi standard and so on.

a company that supports its own limited product range doesn't need newest kernel that much. because contrary to popular belief most kernel changes are not security related. and their devices don't change hardware wise.

but having said all of that if I were you and my device was supported by openwrt, I would probably migrate to openwrt and be free of a small company limited support.

GLiNet has a support page that states if the product is no longer receiving updates. If they are still pushing out updates for it, then I would consider it active.

Even though their OS is based on 21.02, its still their own fork of openwrt. Hopefully theyre back porting security fixes.

https://www.gl-inet.com/support/firmware-versions/

It essentially depends on what level of support you require.

End Of Life is a concept, not generally a fixed point in time .. even though the likes of Microsoft are attempting to rewrite history and making everyone move off Windows 10 by a specific date.

And just like in that situation, you have options.

You can consider your relationship with Microsoft at an end and install a different OS, or you can continue the relationship and buy new hardware even though there's absolutely nothing wrong with what you currently have.

The same is true for a router.

The decision around EOL is about what happens next.

Do you want to yell at the supplier if it breaks, or will you realise that yelling only happens if you spend money on lawyers, and in the meantime you can move on with your life and decide on an alternative path.

My car is worth $700 or so, even though I bought it new 15 years ago. Is it at the end of its life? It's still getting me from here to there and back.