I'm still having the same issue even after following all the solutions listed in this thread. After more investigations, I found out that provisioning profile that has <key>DER-Encoded-Profile</key> fails to install on iOS 15 beta.
XCode beta seems to auto-generate the provisioning profile without this key. However, downloading the provisioning profile from Apple's developer portal has this key and does not let me side load the app.
haroldt
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