If you are one of the 35 (or whatever the roster limit is) but you don't get in any games, you get a redshirt at the end of the year. If the coach has a plan that that is what he's going to do with you, he could tell you up front. Before the pandemic rule changes, I heard of some players that were told that, didn't end well.
The other factor is scholarship:
- if you have an athletic scholarship, you are a counter for the roster limit and practice with the team; if you don't get into a game, you don't use a year of eligibility, i.e. you have been redshirted.
- not all roster counters have athletic scholarships. However, if you are brought in without an athletic scholarship and then not put on the roster, they might call it "redshirting" but you can't practice with the team.
In the current situation, a coach can bring in transfers from jucos and from other 4-year schools. Why would he plan to deliberately redshirt a freshman? Either he thinks he can use you now, or he doesn't. Why would a coach look for future potential, when he can find current skilled players in the transfer portal? He can help them develop, too.
In other words, why would you say to a college coach that you know you will not be good enough to play for him right away?