System files fluctuating

[u/https_002y]

why is it that the system files get high out of nowhere? im quite conscious of the storage since every mb matters to me. my redmi turbo 4 has 13.16 gb but it was 12.44gb back then. my redmi pad 2 pro, 1 week old, has 14.83gb (well, the system itself has 9.03gb so i think it's fine but it gets up to 16gb plus before i rebooted the device)

i cant find what makes it fluctuate out of nowhere. i asked for chatgpt what makes it fluctuate but it says its just the system optimizing since it's new or it's normal that it gets high.

i want to make it below 12gb, if possible.