I found a solution for Windows users.
I have been searching about the same problem for a few days. iTunes make obligation to update itself to iTunes newer version for ios11 phones and iTunes 12.7 versions doesn't have apps section so i couldn't download anymore my ad hoc app ipa file and provision files to iPhone.
I just found out that there is an iTunes version Apple released which won’t be prompted to download new versions of iTunes and you can use this version to download your app. You can dowload it from this link: https://support.apple.com/en-us/HT208079
Apple say if you have a newer version of iTunes you can just download this one over it but I couldn't do it like this. First, I removed iTunes from my computer, then I removed the iTunes folder from my musics folder (you probably don't need to do that) and I downloaded iTunes for 64 bit PC from the link I wrote above. And with this iTunes i can use Apps section again and it doesn't force me to update it. So it is like the good old times again 🙂