Some public lists circulate keys like XXXXX-XXXXX-XXXXX-XXXXX-YMV8X for older Office versions (e.g., Office 2016, 2019). These are almost always:
Most "free" or "cheap" product keys ending in are either Volume License Keys (VLK) intended for large organizations or Generic Volume License Keys (GVLK) . microsoft office product key ending with ymv8x link free