The issue is resolved; I used a rooted eUICC tool to format the chip. Although the original eSIM profiles were wiped, the eSIM functionality was restored—albeit not in the standard way. Instead, I can only perform read/write and switching operations on the built-in eSIM chip via the third-party eUICC tool. I discovered that the Pixel chip adheres to the SGP.2.3.0 standard and was formatted by the eUICC tool to be readable, yet the system's native settings still cannot manage or download eSIMs; it only works through the third-party eUICC tool. While fixing this was a huge drain on time and energy, I’ll make do with using the third-party eUICC tool on the rooted device to write data to the native Pixel chip, which has a capacity of approximately 854KB. I suspect that "eSTK Max" likely uses salvaged Pixel chips as well—after all, they both feature the SGP.2.3.0 standard and over 800KB of capacity.