I tried explicitly setting the target using export TARGET_RELEASE=ap1a and it goes a little further, with the following error:

robotnix-lineage_cheetah> building '/nix/store/9pnnwqhaz86hy9hlsqvf1ayz9fcp0l91-robotnix-lineage_cheetah-2024052404.drv'
robotnix-lineage_cheetah> unpacking sources
robotnix-lineage_cheetah> patching sources
robotnix-lineage_cheetah> building
robotnix-lineage_cheetah> Build type choices are:
robotnix-lineage_cheetah>      1. release
robotnix-lineage_cheetah>      2. debug
robotnix-lineage_cheetah>
robotnix-lineage_cheetah> Which would you like? [1] release
robotnix-lineage_cheetah>
robotnix-lineage_cheetah>
robotnix-lineage_cheetah> Which product would you like? [aosp_arm] lineage_cheetah
robotnix-lineage_cheetah> In file included from build/make/core/config.mk:389:
robotnix-lineage_cheetah> In file included from build/make/core/envsetup.mk:51:
robotnix-lineage_cheetah> build/make/core/release_config.mk:109: error: No release config found for TARGET_RELEASE: trunk_staging. Available releases are: ap1a.
robotnix-lineage_cheetah> 16:15:11 dumpvars failed with: exit status 1
robotnix-lineage_cheetah> ** Not a valid product: lineage_cheetah

i've still been trying to get 21 to build in my free time. Realized that there were some issues with the update script that didn't fully populate device-dirs.json and vendor-dirs.json, specifically get_store_path in robotnix_common.py was returning the path with None/ appended to it. I addressed that, and it seems that the json files are fully populated. I did have to comment out adding a dependency to the vendor file (vendor/google/gs-common) as no repo seems to exist. Not sure where to find that repo. I tried building and now get a nix failure rather than an android build failure:

error:
       … while calling the 'derivationStrict' builtin

         at /builtin/derivation.nix:9:12: (source not available)

       … while evaluating derivation 'cheetah-factory-2024060308.zip'
         whose name attribute is located at /nix/store/d0dl9ch4hhxkqikc1dw3868j95gsbb0h-source/pkgs/stdenv/generic/make-derivation.nix:205:7

       … while evaluating attribute 'buildCommand' of derivation 'cheetah-factory-2024060308.zip'

         at /nix/store/d0dl9ch4hhxkqikc1dw3868j95gsbb0h-source/pkgs/build-support/trivial-builders.nix:74:14:

           73|       name = lib.strings.sanitizeDerivationName name;
           74|       inherit buildCommand;
             |              ^
           75|       passAsFile = [ "buildCommand" ]

       (stack trace truncated; use '--show-trace' to show the full trace)

       error: attribute '"vendor/google/gs-common"' missing

       at /nix/store/d0dl9ch4hhxkqikc1dw3868j95gsbb0h-source/lib/attrsets.nix:107:50:

          106|   */
          107|   getAttrs = names: attrs: genAttrs names (name: attrs.${name});
             |                                                  ^
          108|

Ah yes, sorry:

       error: attribute '"vendor/google/gs-common"' missing

       at /nix/store/d0dl9ch4hhxkqikc1dw3868j95gsbb0h-source/lib/attrsets.nix:107:50:

          106|   */
          107|   getAttrs = names: attrs: genAttrs names (name: attrs.${name});
             |                                                  ^
          108|