I have a GL-MT300A and the latest official release is openwrt-mt300a-2.265 (which has OpenWRT 15.x).
I tried to upgrade to the experimental release for this router (openwrt-mt300a-3.100-1217) but it comes with OpenWRT 18.x. That version had some issues that caused instability on the router.
Is there a way to keep the UI updates and upgrade OpenWRT to 19.x?