My iPhone might have been tapped or tampered with

I have a maybe unique situation. My phone was in an exes possession for approx. 4 days. He wouldn’t have known my Apple ID password, but our daughter is on a family share plan with me and before this happened would use my YouTube account on occasion. Because I change my Apple ID pw regularly I’m unsure if she had access to my account before the phone came into my exes possession. I had my daughters phone at the time (they got switched accidentally), and changed my password from her phone, but not until hours after the switch. When I received the phone back I looked in the settings and the message said it had been charged and backed up just an hour before being returned to me. I know this is probably a boneheaded question to all the tech savvy helpers, but what could this mean in regards to my privacy being compromised? I have since had a few very odd instances with my phone that, in all honesty, when I say them out loud make me sound totally nuts (I’m happy to share if my concern that my phone might have been tapped or tampered with in a significant way is at all valid). If it is, how can I prove something like that, and would it still be relevant, after several months and several password changes later? Thanks

[Re-Titled by Moderator]