There isn’t a widely known “MatePad 10.4” custom ROM scene (e.g., LineageOS, Pixel Experience) because Huawei devices with (like the Kirin 820 in the MatePad 10.4) have locked bootloaders that Huawei no longer provides unlock codes for. This makes installing any custom ROM extremely difficult, if not impossible, for most users.
Since most users want custom ROMs specifically for Google services, you can use these "workarounds" on the stock HarmonyOS or EMUI: huawei matepad 104 custom rom install
