Can the intmax_t hold size_t maximum decimal number? And what size type in printf have a biggest priority uintmax_t/intmax_t or size_t (ex. if i write printf("%zjd", x))?
Most likely not
Both are implementation specific, so it's not really possible to answer.
size_t is (usually) an unsigned integer holding the largest possible number of bits that will fit in a register on a given CPU. That's not exactly guaranteed in reality though, but I still haven't found an example where this isn't true.
intmax_t is a signed integer, meaning it will probably have the bits required to store any value that a size_t can hold, but large values will not mean the same; the largest value that a size_t can hold, is likely going to be a negative integer when interpreted as an intmax_t.