Someone’s icloud was logged in to my device
What will happen if my friends icloud is signed in to my iphone. Can they access all apps installed? Like my messenger, fb and banks?
It depends upon where they signed in and if you provided them with your account information, or if you simply signed out yourself and then let them sign in. If all you did was sign out yourself, they probably can't get into those apps as "you". However, depending upon where they signed in, they could possibly prevent you from using the iPhone, making it useless to you. You may even be able to use it for a while, but eventually it will require they be signed out of the phone or it will lock you out.
I guess I don't really need to say now that you should NEVER, let another person sign into your phone. You are basically giving ownership to them.
Read this document if you think your Apple ID has been compromised. --> If you think your Apple ID has been compromised - Apple Support
For iOS 15 or earlier, if you want to see if anyone else has access to your device or accounts, click here --> Limit access to your iPhone or iPad - Apple Support
For iOS 16 or later see how Safety Check on iPhone works to keep you safe. How Safety Check on iPhone works to keep you safe - Apple Support
Use the information in this document to check your Apple ID device list to find where you're signed in --> Check your Apple ID device list to find where you're signed in - Apple Support
Related materials:
Personal Safety User Guide
Personal Safety User Guide - Apple Support
> open the Table of Contents and review the articles
A document with general information about security and your Apple ID --> Security and your Apple ID - Apple Support
Contact Apple for help with Apple ID account security. This page provides country-specific Apple Support contact information ➞ Contact Apple for support and service - Apple Support