This is not a theoretical risk; it is statistical. Security firms like Kaspersky and Malwarebytes regularly report that third-party app stores host malicious software. When you download a modded APK, you are trusting an anonymous modder.
This is the most critical question.
Many developers offer "Lite" or "Go" versions of their apps (e.g., Spotify Lite, YouTube Music Lite). These use less data and are often ad-free or low-ad. For ad-free YouTube, consider (the legal successor to Vanced), which patches the official YouTube app rather than using a pre-hacked APK. ihappymod