Unfortunately, installing zeptoforth for the PicoCalc means compilation, whether using a kernel UF2 and the included build scripts, or a full UF2 and manually loading each PicoCalc-related source file (which is not the recommended approach, and should only be done if you insist on using Windows and cannot bring yourself to use WSL2).
The reason is that there simply are too many combinations of potential build options for it to be practical for me to build UF2 files for each and every one of them (e.g. graphical vs. text-only, no WiFi vs. zeptoIPv4 vs. zeptoIPv6, five different font options, a variety of underlying zeptoforth builds such as rp2040 vs. rp2040_big vs. rp2350 vs. rp2350_16mib, on-board PSRAM vs. no on-board PSRAM, place the PicoCalc terminal emulator tasks on the second core vs. the first core, etc.).
Furthermore, I on principle do not distribute UF2 files containing CYW43439 firmware (needed for WiFi on the Pico 1W, Pico 2W, and Pimoroni Pico Plus 2W) because to my knowledge the CYW43439 firmware is not properly free, so I distribute it in a separate repository independent of zeptoforth itself and leave it up to the user to load it onto their board.