where is my backup of i phone ios 13.5 on itunes

follow this link

Locate backups of your iPhone, iPad, and iPod touch 

Find a list of your iOS or iPadOS backups on your Mac, PC, and iOS or iPadOS device. Learn how to delete backups, copy them, and more.

https://support.apple.com/en-ca/HT204215

You can also go to iCloud.com to view the contents

You need 3rd party software. The backup is a SQLite database, so you can use a SQLite browser app if you know how to use SQLite. Mere mortals are better of with 3rd party sofware; just do a web search for “iphone backup extractor”, there are several. They are all about the same.

Pmlyons24 wrote:

You can also go to iCloud.com to view the contents

You can’t see the contents of an iCloud backup at iCloud.com, only data that you have synced to iCloud, which is completely separate from an iCloud backup.

I’m afraid you have been led astray. Once a message or message thread is deleted it cannot be recovered, unless both of these conditions are met:

1. You have NOT enabled message syncing to iCloud before the message thread was deleted
2. The message thread is contained in a backup made before the message thread was deleted

It would have been helpful if someone told you this before you went to a lot of trouble.