Thanks DJR85. Started testing with IOS 15, which also has a new code signing requirement. Was getting the developer of this app needs to update it to work with this version of iOS when opening apps already on the device.
Iphonepackager was giving a 0xe8008029 error when validating new installs. I had tried most of the steps but the resigning app. So far only tested a bp-only project on 4.27 and re-signed it on Big Sur. The process isn’t too tedious as you can just transfer the ipa to your device from xcode.