Instagram signin option

Hi im trying to access an old account I made in 2018.

At the time TikTok allowed Instagram sign up, I haven’t been able to access the account for years and it seems the username has since changed for some reason.

I still remember the password but I don’t know the new username (as TikTok changed it for some reason) I never added an email address or phone number as it wasn’t required back then for TikTok using Instagram sign ups.

Has anyone else set up an account this way? How did you fix it

It has videos of me from when I was 12 that I would really like to recover as I lost most the photos and videos of me when I was younger.

Thank you