It's factual that the Cowboys have a long term plan of what to do with Trey Lance. They are following their long-term plan to develop his skills over time and eventually decide whether to keep him on their roster and if so, whether to use him either as a backup or develop him as a starter, assuming his performance measures up to their hopes for his progress. The worst-case scenario is that he'd eventually be cut. Otherwise, he'll be retained on the roster and developed into a backup QB if he's deemed fully qualified for that role. Patience will be dutifully required.
The best-case scenario would be that he's eventually considered worthy of being used as a starting QB or a backup in future years. In the meantime, he must pass many qualifications to finally determine his fate, whatever that might be. It will, of course, require much patience and a willingness to work diligently to develop his skills properly. All of this is likely to require at least 2 years of hard work to satisfy such requirements.