There is an issue with installing apps from the browser in iOS 14 beta (
https://developer.apple.com/forums/thread/652391).
I don't know whether it is a new restriction or just a bug in the beta version.
Once you install B4i-Bridge, it will be able to install other apps.
I have some idea for a workarounds but I'm waiting to first understand whether it is a real issue or not.
For now do this:
Send yourself an email with:
itms-services://?action=download-manifest&url=https://<ip address or hosted builder>:51042/download?type%3Dmanifest_<username>
You need to replace two values: ip address and user name (without the <> chars).
Open the email on your device and click on the link.