As for the KEY2? Keep it as a time capsule. Use it as a dedicated writing device on airplane mode. Or debloat it and accept its security flaws.
The installation process is technical and involves several high-risk steps. LineageOS – LineageOS Android Distribution blackberry key2 lineageos install
You'll need to install ADB and Fastboot tools on your computer, along with USB drivers for your device. As for the KEY2
have seen more development, but even those are highly restricted. Most users looking for a modern QWERTY experience with custom ROM support have moved toward the Unihertz Titan series, which is much more developer-friendly. debloat your KEY2 via ADB to get it as close to a "clean" OS as possible? blackberry key2 lineageos install