Fan games using copyrighted characters (Goku, Vegeta, etc.) exist in a legal gray area. Bandai Namco and Toei Animation have issued takedowns in the past. The developer usually removes active download links voluntarily to avoid lawsuits.
Toei Animation and Bandai Namco aggressively protect their intellectual property. Several Dragon Ball Unreal projects have been mid-development. Any APK you find might be an outdated leak or a build from a project that no longer exists.