Lepton appears to be the new official name for Valve’s version of Waydroid (Android in a Linux container).
We still don’t have a whole lot of details about how this is all going to work, outside of Lepton enabling Android APKs for developers on the upcoming Steam Frame VR kit, but it’s now that little bit more official with a proper name and even a logo.
Pretty sure Waydroid uses the x86 image of LineageOS, cus last time I used it (like a year or more ago) I had to get x86 version of APKs I wanted to install.