What is eating up the Internal Storage of my Xioami phone?

I know, similar posts about this topic have been discussed but reading through them couldn't solve my problem: I have a 5-year-old Redmi note 8 pro (MIUI 12.5.7, Android 11). The internal storage is 64GB of which 42.4GB are occupied but I just cannot find out by what data. I plugged the phone into my Windows 10 pc with the option "show hidden files" activated in Windows Explorer but I still could not see any files that would take that much space. When I select all folders of my internal data in win explorer manually and sum up their size I only get 118MB. I have deleted 1-2GB with DiskUsage but still 40GB remain. The apps I have installed should not occupy more than 10-15GB. So there are still about 25-30gb of unknown files that are swallowing up my phone's storage. How can I find the files that take all the rest of the storage? Also, my internal disk space should be 64GB but windows says I only have 51.3GB which tells me that windows somewhat cannot see everything on my phone.