You might think downloading an old YouTube IPA (the app file) and using a sideloading tool like Sideloadly, AltStore, or TrollStore would work. And sometimes, it does—for a day or two.
For iOS devices, people use:
These tutorials provide step-by-step visual instructions for patching YouTube on various legacy iOS versions: How to fix YouTube on old iOS! (2025 Tutorial) 2K views · 7 months ago YouTube · Tech Pal
Apple has declared war on this. Throughout 2025, Apple has been aggressively revoking certificates within 24 hours of a tweaked YouTube app being detected. When a certificate is revoked, the app crashes on launch immediately. You open YouTube, see a black screen, and the phone says "Untrusted Developer."