update Iphone 12 with ios 17.5

Hi guys

I googled this and found, that I need more than 5gb to do this software update - I now have 11 GB and I can easily download it, but I cant install it the iOS17.5 (from my current iOS 14.5.1). No specific error code, just the "cant install the update" and "there occured an error during the install of iOS 17.5"....what to do?

nb. I already unstalled it, and installed again - but the problem remains...

thanks Apple community