This kind of immutable distros require a very specific partitioning scheme. I tried a couple years ago trying to match the requirements while preserving/reusing my other volumes but it was too finicky and the installation kept failing. I ended up just installing it on its own in a different device that is more fit for purpose (a small PC plugged to my TV). It works great for that use case, but it's not worth experimenting with it beyond that, imho.