After iTunes took backup from iPhone to PC. Where I need to check backed up data in my PC

not sure exactly what you mean

read

Locate backups of your iPhone, iPad, and iPod touch - Apple Support

the backup is 1 big file and one can restore it unto an ios device with the same ios version

Get that it’s one big file but how can I access the photos on my pc for example. How can I review a given file or pic? How do you determine the “big” file location on my pc?

there are several third party backup extractors

Top 6 iPhone Backup Extractor Software List [Free & Paid] (imobie.com)

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iphone backup extractor - Google-