glinet ship their own builds of a forked openwrt (most based on 19.x) containing proprietary patches and binaries. I got a handful of their most recent devices as of last year and all of those are officially still stuck on an ancient 19.x with several security issues that are fixed in upstream but don't make it down.
Got the GL-MT1300 working with a self-built open-source OpenWrt 21.something pretty straightforward but the E750 has been nothing but trouble, weird bugs and unreliability as soon as I try anything except light tweaks of the out-of-box experience. The last thing on the E750 is that my self-built firmware will initially work fine but at some point (and all subsequent boots after), there is not way to get network access either via wired or wifi, despite the OLED indicating everything's as it should. It's in the drawer waiting for me to figure out how to get serial working to debug it as a full factory reset is the only way to recover otherwise and I replicated the issue a few times already.
This is all after several hours of trying to dig apart their convoluted github org to figure out how the builds are made and where the code comes from in the first place.
I'd be really surprise if there will ever be anything 22.03-compatible for any of their current devices given all the iptables voodo in their custom scripts...
Given the combination of poorly maintained official images, inconsistent compatibility with open source upstream, and no way to reproduce their builds, I'd say these can be fun little toys if your use-case perfectly matches the out-of-box provided features but sadly enough you should seriously consider and test each model individually before relying on it for production use even just personally. At least until public progress is made on some of that.