Long story short, my iMac's "other" storage is gigantic and I've been looking through the internet for hours but I couldn't solve my problem. I've been awake for more than 20 hours. I'll post this and then sleep.
By the way, this is my first post. I hope I won't do something wrong.
Here is a starting point; when I had turned off the automatic Time Machine backup option and then restarted the iMac, "other" storage was nearly gone. It had decreased dramatically, like 80 gb disappeared in seconds. After a minute or so, it went all the way up and it, again, became 100+ gb.
Also, now I'm realizing that my free storage is decreasing by time. It was 90+ gb like half an hour ago, now it's 85 gb.
Please, I mean PLEASE help me about this. I need that free storage for Bootcamp, and nothing worked for me. I need any help from you people, please.