What is open source

If you’re simply asking “what is Open Source software” see this wikipedia article for an intro:

https://en.m.wikipedia.org/wiki/Open-source_software

Above answer is correct.

Apple uses open source in various products, and some parts of Apple software are open-source.

You’ll find various open-source-related acknowledgments included in Settings > General > Legal & Regulatory

Additionally… Please consider updating your iPhone XR to iOS 15.7.1 or to iOS 16.1.1; iOS 14 is a ways back.