I created a profile all the way back in 2020, no problems at all. I didn't use the app as much as I do now back then, so I would randomly uninstall it and install it when I feel like doing so. The thing is that, the first time I tried to log back in, it just randomly let me use someone else's account, nothing shady about it other than the fact that it was a fan account for 2 of the worst singers in the world and that the last post had been in 2018. I thought it was pretty odd, but since (I don't really remember how) I was able to log into my account again, I didn't really care about it. But every time I requested a link to my mail so I could log in, it would use the name of that account but lead to my profile. Weirdest fucking thing ever, but I just thought it was a glitch (I was pretty stupid).
Years go by, and I decided to go back to my old account. Again, it gives me the option to log into the random person's profile, and I do just to see if there were any signs of them hacking me. But no, it was still an abandoned account. But I checked to the account center on settings, and it turns out my gmail was actually linked to that account, all along.
I panicked, and I went to my old profile and exported data, to check if anyone had used it all these years. But no, it had been opened just from devices I used. And nothing had changed. And not a single mail showed signs of any stranger using the address for anything. It's basically a family mail, so we would notice after all these years.
I obviously deleted the mail address from the fan account, but I still don't know why it was linked in the first place. Unless they somehow accessed my profile in a way that instagram wouldn't be able to notice, but why to do that if you're not gonna use it at all?