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It is extremely difficult to reverse engineer dexprotector the first time, but it's doable depending on your experience level.
No. Frida is not the easiest way to go. It will poison the dex. Depoisoning is extremely cumbersome and makes it almost impossible to restore HideAccess. There are some aspects where Frida is helpful but they are limited. If you do try to use the frida path, the first step is to restore rtld_db_dlactivity, the linker anti-debug. This function is used by debuggers, including Frida, to track dynamic linker activity.
Guess I should ask how far are you with your research of this protection? Otherwise none of this will make much sense.