The developer agreement states that you're only allowed to sideload apps that you're responsible for developing yourself. Maybe if it's open source you could make an argument for that being allowed, but it's not a general purpose install path for consumers.

Technically true.

> “Application” means one or more software programs (including extensions, media, and Libraries that are enclosed in a single software bundle) developed by You in compliance with the Documentation and the Program Requirements, for distribution under Your own trademark or brand, and for specific use with an Apple-branded product running iOS, watchOS, tvOS, or macOS, as applicable, including bug fixes, updates, upgrades, modifications, enhancements, supplements to, revisions, new releases and new versions of such software programs.

> “Provisioning Profiles” means the files (including applicable entitlements or other identifiers) that are provided by Apple for use by You in connection with Your Application development and testing, and limited distribution of Your Applications for use on Registered Devices and/or on Authorized Test Units.

However in practice, for example, I use the Apple Developer Program with Cydia Impactor to build and install apps like Spike and xDrip on my kids iPhones (they are both T1D). It's basically point and click. [1]

[1] - https://spike-app.com/install-spike-using-cydia-impactor/