The Source code for these Firmwares can be found at the link below.
https://github.com/Envious-Data/EnvKB-QMK/


They can be compiled using this branch of QMK on KarlK90's github as official QMK Support for the RP2040 is WIP.
https://github.com/KarlK90/qmk_firmware/tree/feature/raspberry-pi-rp2040-support

Relevant PR:
https://github.com/qmk/qmk_firmware/pull/14877